U.S. patent number 7,957,807 [Application Number 12/236,852] was granted by the patent office on 2011-06-07 for gastric electrical stimulation with therapy window anti-desensitization feature.
This patent grant is currently assigned to Medtronic, Inc.. Invention is credited to Roland C. Maude-Griffin, Luiz Geraldo Pivotto, Warren L. Starkebaum, Charlene X. Yuan.
United States Patent |
7,957,807 |
Starkebaum , et al. |
June 7, 2011 |
Gastric electrical stimulation with therapy window
anti-desensitization feature
Abstract
The disclosure is directed to gastric stimulation programmers,
stimulators and methods for controlling delivery of gastric
stimulation therapy to maintain the efficacy of the therapy over
time. Maintaining the efficacy of gastric stimulation therapy may
be possible by implementing one or more anti-desensitization
features in a gastric stimulation controller or stimulator. As
electrical stimulation therapy is continuously delivered to a
patient, the stimulated tissue may become desensitized to the
electrical stimulation therapy such that the beneficial effect of
the electrical stimulation is diminished. Once desensitization
occurs, the affected tissue may not respond favorably to electrical
stimulation therapy. Application of one or more
anti-desensitization features to control gastric stimulation
therapy may reduce or prevent desensitization and effectively
extend the efficacy of the therapy over time.
Inventors: |
Starkebaum; Warren L.
(Plymouth, MN), Yuan; Charlene X. (Woodbury, MN),
Maude-Griffin; Roland C. (Edina, MN), Pivotto; Luiz
Geraldo (Geneva, CH) |
Assignee: |
Medtronic, Inc. (Minneapolis,
MN)
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Family
ID: |
40083663 |
Appl.
No.: |
12/236,852 |
Filed: |
September 24, 2008 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20090088818 A1 |
Apr 2, 2009 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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60997058 |
Oct 1, 2007 |
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Current U.S.
Class: |
607/40;
607/133 |
Current CPC
Class: |
A61N
1/36007 (20130101) |
Current International
Class: |
A61N
1/18 (20060101) |
Field of
Search: |
;607/40,133 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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WO/91/06340 |
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May 1991 |
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WO |
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WO 02/28477 |
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Apr 2002 |
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WO |
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WO2007/018786 |
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Feb 2007 |
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WO |
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Other References
Cees de Graaf et al., "Biomarkers of satiation and satiety," Am. J.
Clin. Nut., 2004, vol. 79, pp. 946-961, 2004. cited by other .
U.S. Patent Application entitled "Gastric Electrical Stimulation
With Lockout Interval Anti-Desensitization Feature", U.S. Appl. No.
12/236,836, filed Sep. 24, 2008, Starkebaum et al. cited by other
.
U.S. Patent Application entitled "Gastric Electrical Stimulation
With Multi-Site Stimulation Anti-Desensitization Feature", U.S.
Appl. No. 12/236,924, filed Sep. 24, 2008, Starkebaum et al. cited
by other .
Notification of Transmittal of the International Search Report and
the Written Opinion of the International Searching Authority for
corresponding patent application No. PCT/US2008/011038, mailed Jan.
14, 2008, 17 pages. cited by other .
Valerio Cigaina, MD., "Gastric Pacing as Therapy for Morbid
Obesity: Preliminary Results," Obesity Surgery, vol. 12, No. Suppl.
1, Apr. 1, 2002, 5 pages. cited by other .
Lee et al., "Occupational asthma due to maleic anhydride," Obesity
Surgery, vol. 15, No. 4, Apr. 2005, 3 pages. cited by other .
Lei et al., "Effects and Mechanisms of Implantable Gastric
Stimulation on Gastric Distention in Conscious Dogs," Obesity
Surgery, vol. 15, 2005, pp. 528-533. cited by other .
Reply to Written Opinion for corresponding patent application No.
PCT/US2008/011038, filed Jun. 4, 2009, 4 pages. cited by other
.
Notification of Transmittal of the International Preliminary Report
on Patentability for corresponding patent application No.
PCT/US2008/011038, mailed Sep. 7, 2009, 8 pages. cited by other
.
Office Action for U.S. Appl. No. 12/236,924, mailed May 28, 2010,
10 pages. cited by other .
Response to Office Action for U.S. Appl. No. 12/236,924, filed Aug.
27, 2010, 16 pages. cited by other.
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Primary Examiner: Layno; Carl H
Assistant Examiner: Gedeon; Brian T
Attorney, Agent or Firm: Shumaker & Sieffert, P.A.
Parent Case Text
This application claims the benefit of U.S. provisional application
No. 60/997,058, filed Oct. 1, 2007, the entire content of which is
incorporated herein by reference.
Claims
The invention claimed is:
1. A method comprising delivering electrical stimulation therapy to
a gastrointestinal organ of a patient for a first period of time,
wherein the first period of time is selected to produce a desired
therapeutic effect for a second period of time that extends at
least in part beyond an end of the first period of time, and
wherein the desired therapeutic effect includes a change in gastric
muscle tone indicated by a degree of gastric distention.
2. The method of claim 1, wherein the second period of time is
greater than the first period of time.
3. The method of claim 1, wherein the first period of time is
selected as approximately a minimum period of time sufficient to
produce the desired therapeutic effect for the second period of
time.
4. The method of claim 1, wherein the degree of gastric distention
corresponds to a percentage increase in gastric volume.
5. The method of claim 1, wherein delivering electrical stimulation
therapy to a gastrointestinal organ of a patient for a first period
of time comprises delivering electrical stimulation therapy to one
of a stomach or a small intestine of the patient.
6. The method of claim 1, further comprising receiving an
instruction from an external programmer to generate the electrical
stimulation therapy for the first period of time.
7. A gastric electrical stimulation device comprising: means for
generating electrical stimulation therapy for a first period of
time; and means for delivering the electrical stimulation therapy
to a gastrointestinal organ of a patient, wherein the first period
of time is selected to produce a desired therapeutic effect for a
second period of time that extends at least in part beyond an end
of the first period of time, and wherein the desired therapeutic
effect includes a change in gastric muscle tone indicated by a
degree of gastric distention.
8. The device of claim 7, wherein the second period of time is
greater than the first period of time.
9. The device of claim 7, wherein the first period of time is
selected as approximately a minimum period of time sufficient to
produce the desired therapeutic effect for the second period of
time.
10. The device of claim 7, wherein the degree of gastric distention
corresponds to a percentage increase in gastric volume.
11. The device of claim 7, wherein the gastrointestinal organ is
one of a stomach or a small intestine of the patient, and the
electrical stimulation is configured to produce the desired
therapeutic effect in the stomach or the small intestine.
12. The device of claim 7, further comprising means for receiving
an instruction from an external programmer to generate the
electrical stimulation therapy for the first period of time.
13. A gastric electrical stimulation device comprising: an
electrical stimulation generator that generates electrical
stimulation therapy for a first period of time; and one or more
implantable electrodes coupled to deliver the electrical
stimulation therapy to a gastrointestinal organ of a patient,
wherein the first period of time is selected to produce a desired
therapeutic effect for a second period of time that extends at
least in part beyond an end of the first period of time, and
wherein the desired therapeutic effect includes a change in gastric
muscle tone indicated by a degree of gastric distention.
14. The device of claim 13, wherein the second period of time is
greater than the first period of time.
15. The device of claim 13, wherein the first period of time is
selected as approximately a minimum period of time sufficient to
produce the desired therapeutic effect for the second period of
time.
16. The device of claim 13, wherein the degree of gastric
distention corresponds to a percentage increase in gastric
volume.
17. The device of claim 13, wherein the gastrointestinal organ is
one of a stomach or a small intestine of the patient, and the
electrical stimulation is configured to produce the desired
therapeutic effect in the stomach or the small intestine.
18. The device of claim 13, further comprising a telemetry
interface that receives an instruction from an external programmer
to generate the electrical stimulation therapy for the first period
of time.
19. An external programmer device for a gastric electrical
stimulator, the programmer comprising a processor that controls the
electrical stimulator to generate electrical stimulation therapy
for a first period of time for delivery to a gastrointestinal organ
of a patient, wherein the first period of time is selected to
produce a desired therapeutic effect for a second period of time
that extends at least in part beyond an end of the first period of
time, and wherein the desired therapeutic effect includes a change
in gastric muscle tone indicated by a degree of gastric
distention.
20. The device of claim 19, wherein the second period of time is
greater than the first period of time.
21. The device of claim 19, wherein the first period of time is
selected as approximately a minimum period of time sufficient to
produce the desired therapeutic effect for the second period of
time.
22. The device of claim 19, wherein the degree of gastric
distention corresponds to a percentage increase in gastric
volume.
23. The device of claim 19, wherein the gastrointestinal organ is
one of a stomach or a small intestine of the patient, and the
electrical stimulation is configured to produce the desired
therapeutic effect in the stomach or the small intestine.
24. The device of claim 19, further comprising a telemetry
interface that transmits the instruction to cause the electrical
stimulation generator to generate the electrical stimulation
therapy for the first period of time.
25. A method comprising: selecting a first period of time, for
delivery of electrical stimulation therapy to a gastrointestinal
organ of a patient, sufficient to produce a desired therapeutic
effect for a second period of time that extends at least in part
beyond an end of the first period of time; and controlling an
electrical stimulator to deliver the electrical stimulation therapy
to the gastrointestinal organ of the patient for the first period
of time, wherein the desired therapeutic effect includes a change
in gastric muscle tone indicated by a degree of gastric
distention.
26. The method of claim 25, wherein the first period of time is
selected as approximately a minimum period of time sufficient to
produce the desired therapeutic effect for the second period of
time.
Description
TECHNICAL FIELD
The disclosure relates to implantable medical devices and, more
particularly, implantable medical devices for gastric electrical
stimulation.
BACKGROUND
Obesity is a serious health problem for many people. Patients who
are overweight often have problems with mobility, sleep, high blood
pressure, and high cholesterol. Some other serious risks also
include diabetes, cardiac arrest, stroke, kidney failure, and
mortality. In addition, an obese patient may experience
psychological problems associated with health concerns, social
anxiety, and generally poor quality of life.
Certain diseases or conditions can contribute to additional weight
gain in the form of fat, or adipose tissue. However, healthy people
may also become overweight as a net result of excess energy
consumption and insufficient energy expenditure. Reversal of
obesity is possible but difficult. Once the patient expends more
energy than is consumed, the body will begin to use the energy
stored in the adipose tissue. This process will slowly remove the
excess fat from the patient and lead to better health. Some
patients require intervention to help them overcome their obesity.
In these severe cases, nutritional supplements, prescription drugs,
or intense diet and exercise programs may not be effective.
Surgical intervention is a last resort treatment for some obese
patients who are considered morbidly obese. One common surgical
technique is the Roux-en-Y gastric bypass surgery. In this
technique, the surgeon staples or sutures off a large section of
the stomach to leave a small pouch that holds food. Next, the
surgeon severs the small intestine at approximately mid length and
attaches the distal section of the small intestine to the pouch
portion of the stomach. This procedure limits the amount of food
the patient can ingest to a few ounces and limits the amount of
time that ingested food may be absorbed through the shorter length
of the small intestine. While this surgical technique may be very
effective, it poses significant risks of unwanted side effects,
including malnutrition, and death.
Electrical stimulation therapy is an alternative to surgical
intervention and may be effective in treating obesity either alone
or in combination with diet and exercise. For electrical
stimulation therapy, a patient is fitted with an implanted
electrical stimulator that delivers electrical stimulation pulses
to the patient's stomach via electrodes carried by one or more
leads. The electrical stimulation therapy may be configured to
induce a sensation of fullness or nausea in the patient, thereby
discouraging excessive food intake. In addition, in some cases, the
electrical stimulation therapy may be configured to increase or
decrease gastric motility, reduce appetite or increase satiety, or
induce a sensation of abdominal discomfort on ingestion of a meal,
so that caloric absorption is reduced. Hence, electrical
stimulation therapy may be effective in causing weight loss by
discouraging food intake and/or reducing caloric absorption.
SUMMARY
The disclosure is directed to various techniques for controlling
delivery of gastric electrical stimulation therapy to maintain the
efficacy of the therapy over time. Maintaining the efficacy of
gastric electrical stimulation therapy may be possible by
implementing one or more anti-desensitization features in a gastric
electrical stimulation programmer or gastric electrical stimulator.
The anti-desensitization features may limit application of delivery
of electrical stimulation to selected times, durations,
frequencies, electrode combinations, and/or tissue sites. The
anti-desensitization features may be implemented independently or
in combination with one another to reduce or delay desensitization
of gastric tissue, and thereby promote effective and/or prolonged
therapy.
In one aspect, the disclosure provides a method comprising
receiving a request to deliver gastric electrical stimulation
therapy to a patient, prohibiting delivery of the gastric
electrical stimulation therapy if the request is received within a
lockout period following a previous delivery of the gastric
electrical stimulation therapy, and permitting delivery of the
gastric electrical stimulation therapy if the request is not
received within a lockout period following the previous delivery of
gastric stimulation therapy.
In another aspect, the disclosure provides a system comprising a
stimulator that delivers gastric electrical stimulation therapy to
a patient, and an external programmer that controls the stimulator
to deliver the gastric electrical stimulation therapy, wherein one
of the external programmer or the stimulator receives a request to
deliver the electrical gastric stimulation therapy to the patient,
prohibits delivery of the gastric stimulation therapy by the
stimulator if the request is received within a lockout period
following a previous delivery of gastric stimulation therapy, and
permits delivery of the gastric stimulation therapy by the
stimulator if the request is not received within a lockout period
following the previous delivery of gastric stimulation therapy.
In an additional aspect, the disclosure provides an external
programmer for a gastric electrical stimulator, the programmer
comprising a user interface that receives a request to deliver the
gastric electrical stimulation therapy to a patient, and a
processor that controls the gastric electrical stimulator to
prohibit delivery of the gastric electrical stimulation therapy by
the stimulator if the request is received within a lockout period
following a previous delivery of gastric electrical stimulation
therapy, and permit delivery of the gastric electrical stimulation
therapy by the stimulator if the request is not received within a
lockout period following the previous delivery of gastric
stimulation therapy.
In another aspect, the disclosure provides a gastric electrical
stimulator comprising a stimulation generator that delivers gastric
electrical stimulation therapy, an interface that receives a
request to deliver the electrical gastric stimulation therapy to a
patient, and a processor that controls the stimulation generator
such that the stimulator generator prohibits delivery of the
gastric stimulation therapy by the stimulator if the request is
received within a lockout period following a previous delivery of
gastric stimulation therapy, and permits delivery of the gastric
stimulation therapy by the stimulator if the request is not
received within a lockout period following the previous delivery of
gastric stimulation therapy.
In another aspect, the disclosure provides a method comprising
delivering gastric electrical stimulation therapy from an
implantable gastric electrical stimulator to a patient for a first
period of time, and denying a patient request received by an
external programmer to deliver the gastric electrical stimulation
therapy from the implantable gastric electrical stimulator to the
patient for a lockout period of time following the first period of
time.
In a further aspect, the disclosure provides a method comprising
delivering electrical stimulation therapy to a gastrointestinal
organ of a patient for a first period of time, wherein the first
period of time is selected to produce a desired therapeutic effect
for a second period of time that extends at least in part beyond an
end of the first period of time.
In another aspect, the disclosure provides a gastric electrical
stimulation device comprising an electrical stimulation generator
generates electrical stimulation therapy for a first period of
time, and one or more implantable electrodes coupled to deliver the
electrical stimulation therapy to a gastrointestinal organ of a
patient, wherein the first period of time is selected to produce a
desired therapeutic effect for a second period of time that extends
at least in part beyond an end of the first period of time.
In another aspect, the disclosure provides an external programmer
device for a gastric electrical stimulator, the programmer
comprising a processor that controls the electrical stimulation
generator to generate electrical stimulation therapy for a first
period of time for delivery to a gastrointestinal organ of a
patient, wherein the first period of time is selected to produce a
desired therapeutic effect for a second period of time that extends
at least in part beyond an end of the first period of time.
In another aspect, the disclosure provides a method for gastric
stimulation with reduced desensitization, the method comprising
delivering first electrical stimulation therapy to a
gastrointestinal organ of a patient via a first electrode
combination positioned at a first position on the gastrointestinal
organ for a first period of time greater than or equal to
approximately 30 seconds, and delivering second electrical
stimulation therapy to the gastrointestinal organ via a second
electrode combination positioned at a second position on the
gastrointestinal organ for a second period of time greater than or
equal to approximately 30 seconds, wherein the first and second
electrical stimulation therapies are configured to produce a
substantially identical therapeutic result.
In an additional aspect, the disclosure provides a gastrointestinal
electrical stimulation device comprising a first electrode
combination implantable at a first position on a gastrointestinal
organ of a patient, a second electrode combination implantable at a
second position on the gastrointestinal organ, and a stimulation
generator that delivers first electrical stimulation therapy to the
gastrointestinal organ via the first electrode combination for a
first period of time greater than or equal to approximately 30
seconds, and delivers second electrical stimulation therapy to the
gastrointestinal organ via a second electrode combination for a
second period of time greater than or equal to approximately 30
seconds, wherein the first and second electrical stimulation
therapies are configured to produce a substantially identical
therapeutic result.
The details of one or more embodiments of the disclosure are set
forth in the accompanying drawings and the description below. Other
features, objects, and advantages of the disclosure will be
apparent from the description and drawings, and from the
claims.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a schematic diagram illustrating an example implantable
gastric electrical stimulation system.
FIG. 2 is a block diagram illustrating example components of an
implantable gastric electrical stimulator that delivers gastric
electrical stimulation therapy.
FIG. 3 is a block diagram illustrating example components of a
patient programmer that receives patient input and communicates
with a gastric electrical stimulator.
FIG. 4 is a conceptual diagram illustrating example electrode
arrays positioned on the stomach of the patent for delivery of
gastric electrical stimulation.
FIGS. 5A-5E are example timing diagrams illustrating different
modes for delivering electrical stimulation pulses.
FIG. 5F is a graph illustrating gastric distention during and
following application of stimulation within a therapy window.
FIGS. 6A, 6B and 6C are example timing diagrams illustrating
continuous pulses and bursts of pulses delivered to the patient via
two different channels.
FIGS. 7A, 7B, 7C, 7D, and 7E are example timing diagrams
illustrating relative timing of stimulation delivered via different
channels.
FIGS. 8A, 8B and 8C are example timing diagrams illustrating bursts
of pulses having variations between bursts.
FIG. 9 is a flow diagram illustrating a method for delivering
gastric stimulation therapy according to a lockout period that
extends the efficacy of the therapy.
FIG. 10 is a flow diagram illustrating a method for delivering
gastric electrical stimulation therapy according to a combination
of electrodes selected to extend the efficacy of the therapy.
FIG. 11 is a flow diagram illustrating a method for delivering
gastric electrical stimulation therapy at randomized start times to
extend the efficacy of the therapy.
FIG. 12 is a flow diagram illustrating a method for selecting
different burst pattern characteristics for gastric electrical
stimulation to extend efficacy of therapy.
FIG. 13 is a flow diagram illustrating application of a therapy
window feature for gastric electrical stimulation to extend
efficacy of therapy.
FIG. 14 is a flow diagram illustrating application of a multi-site
stimulation feature for gastric electrical stimulation to extend
efficacy of therapy.
DETAILED DESCRIPTION
The disclosure is directed to techniques for controlling delivery
of gastric stimulation therapy to maintain the efficacy of the
therapy over time. Maintaining the efficacy of gastric stimulation
therapy may be possible by implementing one or more
anti-desensitization features in an external gastric stimulation
programmer and/or gastric electrical stimulator to limit
application of electrical stimulation to selected frequency, times,
tissue sites, and/or durations. The anti-desensitization features
may be implemented independently or in combination with one another
to reduce or delay desensitization of gastric tissue, and thereby
promote effective and/or prolonged therapy.
The gastric stimulator may be external or implantable. An external
stimulator may deliver stimulation via one or more percutaneously
implantable leads. An implantable stimulator may deliver
stimulation via one or more fully implantable leads. An external
programmer such as a patient programmer or physician programmer may
communicate with a gastric electrical stimulator, e.g., by radio
frequency (RF) wireless telemetry or other techniques. Gastric
electrical stimulation generally refers to electrical stimulation
of the stomach, small intestine or other organs within the
gastrointestinal tract, and may alternatively be referred to as
gastrointestinal electrical stimulation.
Desensitization may generally refer to a state of accommodation in
which delivery of electrical stimulation to a particular tissue
site is less effective in achieving a desired therapeutic result.
Incorporation of anti-desensitization features in a programmer
and/or stimulator may allow gastric stimulation therapy to be more
effective in treating the patient for a longer period of time when
compared to standard therapy. This extended period of effective
therapy may reduce the chance that the patient will need to pursue
different treatment options due to electrical stimulation
desensitization. In addition, in some cases, one or more
anti-desensitization features may reduce the amount and duration of
stimulation provided to the patient, which may conserve battery
power and extend the operational life of an implantable
stimulator.
As electrical stimulation therapy is continuously delivered to a
patient, the stimulated tissue may become desensitized to the
electrical stimulation therapy such that the beneficial effect of
the electrical stimulation is diminished. Once desensitization
occurs, the affected tissue may no longer respond favorably to
electrical stimulation therapy. Application of one or more
anti-desensitization features to control gastric stimulation
therapy, either via an external gastric stimulation programmer or
an implantable gastric stimulator, or both, may reduce or prevent
desensitization and effectively extend the efficacy of the therapy
over time.
In accordance with this disclosure, an external gastric stimulation
programmer or gastric electrical stimulator may utilize one or more
anti-desensitization features that extend the efficacy of gastric
stimulation therapy delivered to the patient by the gastric
stimulator. The external gastric stimulation programmer may be, in
some cases, a patient programmer that communicates within the
gastric stimulator, e.g., by wireless telemetry. The
anti-desensitization features may include at least one of a lockout
period feature, a therapy window feature, a multi-site stimulation
feature, a therapy schedule feature, a burst pattern variation
feature, and a burst pattern parameter selection feature.
After therapy has been delivered for a permitted period of time,
either by way of a therapy window feature or otherwise, a lockout
period feature may be applied by the programmer or stimulator to
prevent the patient from reinitiating further stimulation therapy
until the lockout period expires, thus preventing excessively
frequent stimulation. If a patient attempts to reactivate
stimulation before the lockout period has expired, the programmer
or stimulator may prohibit delivery of stimulation. In addition,
the programmer may notify the patient that stimulation cannot be
activated until the lockout period has expired.
The length of the lockout period may be selected to ensure that
subject tissue has a sufficient period of time to recover between
successive applications of electrical stimulation in order to avoid
or delay desensitization. The lockout period may be, for example,
on the order of several seconds, minutes or hours. The lockout
period feature may interrupt stimulation for certain periods of
time, which may allow time for neurotransmitters to be replenished
at the cell level.
Upon receipt of a request to delivery stimulation therapy, a
programmer or stimulator may apply the lockout period feature to
prohibit delivery of the gastric electrical stimulation therapy if
the request is received within a lockout period following a
previous delivery of the gastric electrical stimulation therapy,
and deliver the gastric electrical stimulation therapy if the
request is not received within a lockout period following the
previous delivery of gastric stimulation therapy.
Using a therapy window feature, the programmer or stimulator may
permit delivery of therapy for only a relatively short duration
such that the patient may rely upon residual stimulation effects to
prolong a desired therapeutic effect after stimulation has been
stopped. In this manner, the therapy window prevents stimulation
for an excessive period of time. In some cases, the therapy window
W may represent approximately a minimum duration of the gastric
stimulation therapy that has been determined or estimated to be
effective in producing desired therapeutic effects for a desired
period of time, including a period of time after termination of the
gastric stimulation therapy. In some cases, the therapy window W
may represent approximately the minimum duration plus a time margin
to ensure the desired therapeutic effect for the desired period of
time.
At the same time, although it may be determined as a function of
the minimum duration sufficient to produce a therapeutic effect for
a desired period of time, the therapy window W also may specify the
maximum period for which stimulation may be delivered at a given
time. If the minimum duration defining the therapy window W is
sufficient to achieve a desired therapeutic effect for a given
period of time, then delivery of stimulation beyond this duration
may be considered inefficient. Accordingly, the therapy window W
may specify the maximum duration of stimulation to be delivered,
and at the same time be determined according to the minimum
duration sufficient to achieve a desired therapeutic effect for a
specified period of time.
If the minimum period of time sufficient to maintain a desired
therapeutic effect for a desired period of time x, given a set of
stimulation parameters, is y minutes, then the therapy window W may
be approximately y minutes in length, possibly plus or minus a
margin of time. Hence, when the stimulator delivers stimulation
during the therapy window W, it may deliver stimulation for a
maximum of y minutes. However, the therapeutic effect may be
produced for x minutes. Application of stimulation for the length
of the therapy window W, with appropriate stimulation parameters,
may be sufficient to cause a desired therapeutic effect that
remains at least partially intact for a prolonged period of time
even after delivery of stimulation is terminated. In this case, a
desired therapeutic effect can be achieved for an extended period
of time beyond the actual time that electrical stimulation is
applied to the patient.
To implement the therapy window feature, a programmer or stimulator
may deliver electrical stimulation therapy to a gastrointestinal
organ of a patient for a first period of time, wherein the first
period of time is selected to produce a desired therapeutic effect
for a second period of time that extends at least in part beyond an
end of the first period of time. In this case, the first period of
time corresponds to the therapy window W, and the second period of
time corresponds to the period of time for which the desired
therapeutic effect persists. The second period of time, in some
cases, may be greater than the first period of time. The first
period of time may be selected, in some cases, as approximately a
minimum period of time sufficient to produce the desired
therapeutic effect for the second period of time. As an example,
the desired therapeutic effect may be a change in gastric muscle
tone indicated by a degree of gastric distention. The degree of
gastric distention may correspond to a percentage increase in
gastric volume.
The programmer or stimulator may apply a therapy schedule feature
to permit delivery of stimulation therapy only during predetermined
therapy schedule times S, e.g., coincident with ordinary meal or
snack times for obesity therapy or motility regulation. The therapy
schedule may be customized for particular patients to match
different meal times, snack times and lifestyles. Therapy windows W
may be applied at different times within a permitted schedule time
S. Notably, the schedule time S is different from the first and
second periods referred to above with respect to the therapy window
feature, as well as the lockout period described above. In
contrast, the schedule times specify times on a schedule at which
stimulation may be delivered, possibly subject to other
anti-desensitization features such as the lockout period and
therapy window features.
When delivery of stimulation therapy is requested at a time that
does not fall within one of the predetermined therapy schedule time
S on the therapy schedule, the programmer or stimulator may
prohibit delivery of stimulation therapy. In addition, the
programmer may notify the patient that stimulation cannot be
activated until the next permitted time S on the therapy schedule.
Hence, stimulation may be off between therapy time S on the therapy
schedule, helping to prevent or delay desensitization of stimulated
tissue. Delivery of stimulation therapy may be requested by a
patient or requested internally within a programmer or stimulator
as an automated request, e.g., according to a therapy schedule.
Using a multi-site stimulation feature, the programmer or
stimulator may select different combinations of electrodes to
deliver stimulation to different tissue sites at different times.
The different times may partially overlap or not overlap. The
multi-site stimulation feature may be applied such that different
electrode combinations are used within a therapy window W, or
within different therapy windows, or within different periods of
time on the therapy schedule, or when stimulation is otherwise
applied. In this manner, the programmer or stimulator may
distribute electrical stimulation over a larger number of varied
tissue sites over time to prevent rapid desensitization that could
otherwise occur if stimulation was delivered to a single tissue
site. In some cases, the selection of different electrode
combinations for stimulation at different times may be ordered,
randomized, or pseudo-randomized such that stimulation is delivered
to different tissue sites over time in order to prevent or delay
desensitization of a particular tissue site.
As an example, to implement an multi-site stimulation feature, a
programmer or stimulator may control delivery of gastric
stimulation by delivering first electrical stimulation therapy to a
gastrointestinal organ via a first electrode combination associated
with a first position on the gastrointestinal organ for a first
period of time, and delivering second electrical stimulation
therapy to the gastrointestinal organ via a second electrode
combination associated with a second position on the
gastrointestinal organ for a second period of time. The periods of
time used for the multi-site stimulation feature, like the periods
used for the lockout period and therapy window, are different from
the therapy schedule periods P.
The electrode combinations used for the multi-site stimulation
feature, may be associated with the positions on the
gastrointestinal organ in the sense that electrodes in the
combinations are generally co-located with the positions, or
otherwise positioned to direct stimulation to the positions as
different stimulated tissue sites. In some cases, however, each
electrode combination may include at least one electrode in common
with one another, e.g., such as a common ground electrode on a
device housing in a unipolar arrangement or elsewhere in a bipolar
or multipolar arrangement. In addition, at least some of the
electrodes forming an electrode combination may be carried by the
same lead or different leads.
In some examples, each of the first and second periods of time may
be greater than or equal to approximately 30 seconds. In this
manner, stimulation may be applied to a tissue site for a period of
time sufficient to support a desired therapeutic effect, but then
be shifted to another tissue site to mitigate tissue
desensitization. In other cases, each of the first and second
periods of time may be greater than or equal to approximately one
minute, five minutes, one hour, or one day. The first and second
periods may reside within different therapy windows W or different
schedule periods P, or within the same therapy windows W or
schedule periods P.
The first and second electrical stimulation therapies delivered to
different tissue sites are configured to produce a substantially
identical therapeutic result, such as promotion of gastric
distention, nausea or discomfort to discourage food intake by a
patient. In other words, each electrode combination delivers
stimulation with parameters selected to produce substantially the
same result, such as gastric distention. In some cases, the first
and second electrical stimulation therapies may be configured to
reduce, increase, or maintain gastric motility. In other cases, the
first and second stimulation therapies are configured to not
reduce, increase, or maintain gastric motility, and instead to
promote gastric distention, nausea or discomfort, as mentioned
above.
Using the multi-site feature, the programmer or stimulator may
control delivery of stimulation via two or more different electrode
combinations, e.g., on an interleaved basis during a given therapy
window W or during different therapy windows. In this manner, the
stimulation therapy is distributed among different tissue sites as
it is delivered to prevent rapid desensitization at a single tissue
site. For example, stimulation may be delivered to a first
electrode combination associated with a first tissue site and then
delivered to a second electrode combination associated with a
second tissue site, e.g., as interleaved, alternating pulse trains,
bursts, or the like, within a given therapy window or therapy
period. As mentioned above, the stimulation parameters, electrode
combinations and associated tissue sites may be selected to support
a substantially similar therapeutic effect, yet reduce the amount
of time each of the tissue sites receives stimulation, thereby
preventing of delaying desensitization.
The programmer or stimulator may apply a burst pattern variation
feature as a further anti-desensitization feature to vary the
timing and/or duration of burst patterns of stimulation delivered
to a patient. A pulse burst generally refers to a group of
stimulation pulses, e.g., by gating a continuous pulse train on and
off. During the ON period, a pulse burst is produced. A burst
pattern, as used herein, generally refers to a set of multiple
pulse bursts. To reduce or delay desensitization, burst patterns
can be produced by gating bursts ON and OFF. During the ON period,
the stimulator delivers bursts of pulses. During the OFF period, no
pulses or bursts are delivered. The pulse bursts can be gated ON
and OFF repeatedly throughout the day to deliver burst patterns at
selected times. The timing and/or duration of the burst patterns
may be fixed during the day or varied. In either case, delivery of
selected burst patterns instead of continuous bursts or continuous
pulse trains may be effective in treating as well as in preventing
or delaying desensitization.
With the burst pattern parameter selection feature, the programmer
or stimulator may vary one or more stimulation parameter values
over a series of burst patterns, as described above. For example,
instead of delivering stimulation in continuous pulses, or bursts
of pulses, the programmer or stimulator may control stimulation
such that it is delivered in burst patterns, wherein each burst
pattern includes multiple pulse bursts and each burst pattern is
separated in time from another burst pattern. The programmer or
stimulator may vary stimulation parameters such as amplitude, pulse
width, and pulse rate of pulses among different burst patterns as
another anti-desensitization feature, e.g., to prevent or delay
desensitization of stimulated tissue.
The anti-desensitization features described above may be applied by
a programmer, a stimulator or both to limit or prevent
desensitization. In addition, the anti-desensitization features may
be used individually or in combinations of two, three or more
additional anti-desensitization features to extend or maintain
efficacious therapy by preventing rapid desensitization. In some
cases, some or all of the anti-desensitization features may be
applied by the programmer, stimulator, or both. Also, in some
embodiments, one or more anti-desensitization features may be
applied by the programmer while one or more other
anti-desensitization features may be applied by the stimulator. The
anti-desensitization features may be applied by a programmer in
selectively controlling a stimulator via commands or requests
transmitted to the stimulator, and may be applied by a stimulator
by controlling stimulation generated by the stimulator.
In general, the disclosure is directed to methods for controlling
delivery of gastric electrical stimulation therapy to maintain the
efficacy of the therapy over time. Gastric electrical stimulation
therapy may be delivered to the gastrointestinal tract, e.g., the
stomach and/or small intestine, to treat a disease or disorder such
as obesity or gastroparesis. In the case of obesity therapy, for
example, electrical stimulation of the stomach may be configured to
cause the stomach to undergo a change in gastric muscle tone, which
may be indicated by distention, and induce a feeling of satiety
within the patient. As a result, the patient may reduce caloric
intake because the patient has a reduced urge to eat.
Alternatively, or additionally, electrical stimulation of the
stomach may be configured to induce nausea in the patient and
thereby discourage eating. In addition, electrical stimulation of
the duodenum may be configured to increase motility in the small
intestine, thereby reducing caloric absorption. For gastroparesis,
gastric stimulation of the stomach and/or duodenum may be
configured to increase or regulate motility. In each case, however,
consistent electrical stimulation of the same tissue over time may
desensitize the tissue to the electrical stimulation, resulting in
accommodation and reduced therapeutic efficacy.
Patients receiving implantable gastric stimulators may report an
initial sensation that subsides over time. One explanation is that
one or more neurotransmitters necessary for depolarization of a
nerve or muscle cell may become depleted over time when a nerve or
muscle cell is stimulated continuously over time. There may be
insufficient time for this neurotransmitter to be replenished to a
level sufficient for the nerve or muscle cell to fire in response
to electrical stimulation. This resulting desensitization may cause
diminished efficacy of the electrical stimulation therapy to a
point where the therapy is no longer beneficial in treating the
patient. For this reason, it may be beneficial to implement one or
more anti-desensitization features in the control of the delivery
of the therapy, either in a programmer or stimulator, to maintain
the efficacy of the therapy.
One or more of the anti-desensitization features described in this
disclosure may prevent or delay desensitization while also allowing
the patient to initiate the gastric stimulation therapy. A
clinician may set the anti-desensitization features when initially
programming the gastric stimulation therapy or at any time
throughout the duration of therapy. For example, a programmer may
present a menu for the clinician to select one or more desired
anti-desensitization features to be applied to the stimulator
individually or in various combinations. In some embodiments, the
patient programmer may permit a patient to control the stimulator
to start delivery of gastric stimulation therapy, stop delivery of
gastric stimulation therapy, and/or adjust one of more parameters
associated with gastric stimulation therapy. In other cases, the
patient may have limited control or no control over the gastric
stimulation therapy.
The patient programmer and stimulator may operate in a cooperative
or complementary manner. The patient programmer may not permit the
patient to control the stimulator in violation of the lockout
period, therapy window, and/or therapy schedule. Alternatively, the
stimulator may deny commands received from the programmer that
would violate the lockout period, therapy window, and/or therapy
schedule. Even if delivery of stimulation is permitted, consistent
with therapy windows, therapy schedules, and lockout periods, the
programmer or stimulator may implement a burst pattern variation
feature, a multi-site stimulation feature, and/or a burst pattern
parameter selection feature as described in this disclosure.
For example, the stimulator may automatically apply the therapy
window feature, multi-site stimulation feature, burst pattern
variation feature, and/or burst pattern parameter selection feature
when delivering stimulation therapy pursuant to a request from the
programmer. Alternatively, when the programmer requests therapy, it
may further specify application of a therapy window feature, burst
pattern variation feature, multi-site stimulation feature, and/or
burst pattern parameter selection feature by the stimulator. In
some cases, the programmer may specify the particular electrodes,
channels, and stimulation parameters to be applied by the
stimulator in supporting the therapy window feature, multi-site
stimulation feature, and/or a burst pattern parameter selection
feature.
The various techniques and features described in this disclosure
may be implemented within an external programmer, an external or
implantable gastric electrical stimulator, or a combination of
both. The external programmer may be a patient programmer that
accompanies a patient through a daily routine. Various examples of
programmers, stimulators and associated functionality are provided
for illustration, but without limitation of the various aspects of
the disclosure as broadly embodied and described herein.
FIG. 1 is a schematic diagram illustrating an example implantable
gastric stimulation system 10. System 10 is configured to prevent
desensitization of a patient 16 to the gastric stimulation therapy.
System 10 delivers gastric stimulation therapy to patient 16 in the
form of electrical stimulation. Patient 16 may be a human or
non-human patient. However, system 10 will generally be described
in the context of delivery of gastric stimulation therapy to a
human patient, e.g., to treat obesity or gastroparesis. Gastric
distention may generally refer to an increase in gastric volume or
a relaxation in gastric muscle tone. Hence, a volumetric change
associated with gastric distention may be indicative of a state or
relaxation of gastric muscle tone. In general, in accordance with
this disclosure, gastric distention, increase in gastric volume and
relaxation of gastric muscle tone may be used interchangeably to
generally refer to a relative state of contraction or relaxation of
the stomach muscle.
The state of contraction or relaxation of the stomach muscle may be
evaluated using a device called a balloon barostat. The Distender
Series II.TM., manufactured by G&J Electronics, Inc., Toronto,
Ontario, Canada, is an example of a balloon barostat system that
may be used to diagnose certain gastric motility disorders. Using
this system, a balloon is inserted into the stomach, and inflated
to a pressure just above the abdominal pressure, referred to the
minimum distending pressure. The barostat is configured so that the
pressure in the balloon is maintained at a constant pressure. If
the state of contraction of stomach muscle decreases, i.e., the
state of relaxation of the stomach muscle increases, then the
balloon volume will increase. A decrease in the state of stomach
muscle contraction, if measured under conditions of constant
balloon pressure, indicates a change in gastric muscle tone, i.e.,
gastric muscle relaxation, and is sometimes referred to as a change
in gastric distention, gastric volume, or gastric tone. More
particularly, a decrease in muscle contraction corresponds to an
increase in muscle relaxation and promotes distention in terms an
increase in gastric volume using balloon barostat evaluation.
Gastric stimulation therapy is generally described herein as being
provided to cause gastric distention, which may be associated with
an increase in gastric volume and indicate an increase in gastric
muscle tone relaxation. Alternatively or additionally, gastric
stimulation therapy may be delivered by system 10 to induce nausea,
cause regurgitation, or cause other actions to treat certain
patient disorders. In other embodiments, gastric stimulation
therapy parameters may be selected to induce or regulate gastric
motility, while in other embodiments the gastric stimulation
therapy parameters are selected not to induce or regulated gastric
motility but to promote gastric distention.
Inducing gastric distention in patient 16 causes the volume of
stomach 22 to increase, simulating a full or fuller stomach, and
causing patient 16 to feel prematurely satiated before or during
consumption of a meal. Increased gastric distention and volume are
generally consistent with a decreased state of stomach muscle
contraction, which conversely may be referred to as an increased
state of stomach muscle relaxation. While gastric stimulation
therapy is shown in this disclosure to be delivered to stomach 22,
the gastric stimulation therapy may be delivered to other portions
of patient 16, such as the duodenum or other portions of the small
intestine.
As shown in FIG. 1, system 10 may include an implantable stimulator
12 and an external patient programmer 14, both shown in conjunction
with a patient 16. Implantable stimulator 12 may be referred to
generally as an IMD. Patient programmer 14 and stimulator 12 may
communicate with one another to exchange information such as
commands and status information via radio frequency (RF) wireless
telemetry. Stimulator 12 includes an electrical stimulation
generator that generates electrical stimulation pulses or
continuous signals. For purpose of illustration, however, and
without limitation, pulses will be generally described herein. In
some embodiments, system 10 may further include a drug delivery
device that delivers drugs or other agents to the patient for
obesity or gastric motility therapy, or for other nongastric
related therapies. One or more implantable leads 18, 20 carry the
electrical stimulation from stimulator 12 to stomach 22. In other
embodiments, stimulator 12 may be formed as an RF-coupled system in
which an external controller provides both control signals and
inductively coupled power to stimulator 12 within patient 16. Also,
in alternative embodiments, system 10 may use an external, rather
than implanted, stimulator, e.g., with percutaneously implanted
leads and electrodes.
Leads 18, 20 each may include one or more electrodes 24, 26 for
delivery of the electrical stimulation pulses to stomach 22. In the
case of multiple electrodes attached to each lead 18, 20, the
multiple electrodes may be referred to as an electrode array.
Combinations of two or more electrodes on one or both of leads 18,
20 may form bipolar or multipolar electrode pairs. For example, two
electrodes on a single lead may form a bipolar arrangement.
Similarly, one electrode on a first lead and another electrode on a
second lead may form a bipolar arrangement. Various multipolar
arrangements also may be realized. A single electrode 24, 26 on
leads 18, 20 may form a unipolar arrangement with an electrode
carried on a housing of stimulator 12. Although the electrical
stimulation, e.g., pulses or continuous waveforms, may be delivered
to other areas within the gastrointestinal tract, such as the
esophagus, duodenum, small intestine, or large intestine, delivery
of stimulation pulses to stomach 22 will generally be described in
this disclosure for purposes of illustration. In the example of
FIG. 1, electrodes 24, 26 are placed in lesser curvature 23 of
stomach 22. Alternatively, or additionally, electrodes 24, 26 could
be placed in the greater curvature of stomach 22 or at some other
location around stomach 22.
As mentioned above, gastric distention tends to induce a sensation
of fullness and thereby discourages excessive food intake by the
patient. The therapeutic efficacy of gastric electrical stimulation
in managing obesity depends on the stimulation parameters and
stimulation target. Electrical stimulation may have mechanical,
neuronal and/or hormonal effects that result in a decreased
appetite and increased satiety. In turn, decreased appetite results
in reduced food intake and weight loss. Gastric distention, in
particular, causes a patient to experience a sensation of satiety
due to expansion of the stomach, biasing of stretch receptors, and
signaling fullness to the central nervous system.
While electrical stimulation to stomach 22 may cause gastric
distension, tissue stimulated by the electrical pulses may not
continue to react in substantially the same manner after many
pulses are delivered over a period of time. Electrical stimulation
to the same tissue over an extended period of time such as hours,
days or weeks may decrease the effectiveness of the stimulation to
the tissue. In particular, the tissue may become desensitized or
accommodating of the stimulation therapy. Therefore, the therapy
becomes less effective to the point that patient 16 receives no
further benefit from stimulating the same tissue. System 10 may
include one or more anti-desensitization features, implemented by
programmer 14, stimulator 12, or both. The features may be designed
to reduce the extent of desensitization, or prevent or delay
desensitization of stimulated tissue. The anti-desensitization
features may extend the efficacy of gastric stimulation therapy
delivered to the patient.
Reducing desensitization may involve limiting the amount of
simulation delivered to a specific tissue of stomach 22 over time.
It may not be necessary to provide gastric stimulation therapy
throughout the majority of the day for patient. Instead,
stimulation therapy may be patient-initiated when patient 16 feels
hungry and requires therapy to avoid ingesting excessive calories.
In this manner, stimulation therapy may only be delivered to
stomach 22 when needed.
One example anti-desensitization feature may be a lockout period
that prevents patient programmer 14 from directing stimulator 12 to
deliver gastric stimulation therapy upon receiving an indication
from patient 16 to start therapy. The lockout period may begin when
stimulation therapy begins or when stimulation therapy is turned
off. Generally, the lockout period may be between approximately 5
and 240 minutes. More specifically, the lockout period may be
between approximately 30 and 120 minutes. The lockout period may
vary in duration depending upon the frequency of stimulation, the
duration of stimulation, the time of day, patient condition, or
other variables that may effect the desired lockout period. For
example, the lockout period may be 60 minutes between 7:00 AM and
12:00 PM, 90 minutes between 12:00 PM and 5:00 PM, and 120 minutes
between 5:00 PM and 7:00 AM. The lockout periods may also change
through the duration of therapy to prevent patient 16 from adapting
to the lockout period and circumventing therapy.
In operation, the patient may initiate delivery of electrical
stimulation therapy by stimulator 12 via patient programmer 14 for
a permitted period of time, which may be referred to as a therapy
window W, and which may constitute another type of
anti-desensitization feature. The period of time could be, for
example, one to two hours to cover an ordinary meal time. In
addition, the period of time may be selected based on a therapy
window desensitization feature, as described elsewhere in this
disclosure. Following a start of the delivery of the gastric
electrical stimulation therapy, delivery of the gastric electrical
stimulation therapy may be terminated upon expiration of the
therapy window. After applying the stimulation therapy for the
permitted period of time, patient programmer 14 would institute the
lockout period feature such that the patient 16 is prohibited from
restarting stimulation for a specified period of time (the lockout
period) following termination of electrical stimulation therapy. As
an illustration, if stimulation was active for a permitted period
of time of one hour, e.g., as specified by a therapy window or
otherwise, following termination of the stimulation the patient 16
would not be permitted to restart stimulation for the duration of a
lockout period, e.g., 30 to 120 minutes, running from the end of
the previous stimulation period.
Patient programmer 14 may be configured to start a clock or other
timing device following termination of the electrical stimulation
therapy in order to time the lockout period. Once the lockout
period has elapsed, patient programmer 14 may permit patient 16 to
recommence delivery of electrical stimulation therapy. In
particular, if the lockout period is expired, an attempt by the
patient 16 to initiate therapy via patient programmer 14 would be
successful and the patient programmer would send an appropriate
command to stimulator 12 to start therapy. If the attempt is made
during the lockout period, however, patient programmer 14 would not
send a command to stimulator 12 to start delivery of therapy.
Instead, patient programmer 14 may generate a message to the
patient 16 indicating that the lockout period is in effect.
As an alternative, stimulator 12 may start a clock or timing
device, and be configured to refuse to accept or carry out an
additional therapy start command from programmer 14 until a lockout
period tracked by such a timing device has expired. Hence, the
lockout period feature may be implemented in programmer 14, by
refusing to transmit a stimulation start command to stimulator 12
if the stimulation request is received within an active lockout
period tracked by the programmer. Alternatively, stimulator 12 may
implement the lockout period feature by refusing to start
stimulation in response to a stimulation start command from
programmer 14 if the command is received within an active lockout
period tracked by the stimulator. In this case, the stimulator 12
may receive the request from the patient via an external programmer
via wireless telemetry. Stimulator 12 then may communicate the
refusal to programmer 14, e.g., by wireless telemetry.
In either case, whether the lockout feature is enforced by
stimulator 12 or programmer 14, the programmer 14 may notify the
patient 16 that the lockout period is active and that stimulation
cannot be restarted. The notification may be communicated by
audible, visual, and/or tactile media, such as a speaker, display
or buzzer. In some embodiments, programmer 14 may notify the
patient 16 of the lockout and advise the patient of the time at
which the lockout period will expire. In other cases, programmer 14
may indicate a running time or countdown of the lockout period,
e.g., on a display or other user interface feature, which may
discourage the patient 16 from even trying to start stimulation
during the lockout period. Hence, a user interface of the
programmer 14 may indicate at least one of a running time, a
countdown, or an expiration time of the lockout period to a
user.
With the lockout feature, a external programmer or an implantable
gastric electrical stimulator may control delivery of gastric
electrical stimulation therapy from an implantable gastric
electrical stimulator to a patient for a first period of time, but
deny a patient request received by an external programmer to
deliver the gastric electrical stimulation therapy from the
implantable gastric electrical stimulator to the patient for a
second period of time following the first period of time. In this
case, the second period of time is the lockout period. The patient
request may be received and processed by the patient programmer to
impose the lockout period feature. Alternatively, the patient
request received by the external programmer may be transmitted to
the implantable gastric electrical stimulator, which then processes
the request to apply the lockout period feature.
Another example anti-desensitization feature is a therapy window
that defines the duration of electrical stimulation. The therapy
window may be enforced by stimulator 12, programmer 14, or both.
Once gastric stimulation is started, the therapy window may limit
the duration of the stimulation to the length of the window in
order to limit the amount of stimulation delivered to the tissue.
Generally, the therapy window may be between approximately 1 and 60
minutes in duration. More specifically, the therapy window may be
between approximately 3 and 30 minutes in duration. Shorter or
longer therapy windows may be necessary to treat patient 16,
depending upon stimulation parameters and patient condition.
Different therapy windows, i.e., of different lengths, may be
predetermined for different therapeutic effects and different
periods of time for which the therapeutic effects are desired.
Accordingly, when a desired therapeutic effect is desired for a
particular period of time, the effect and the time can be mapped to
an appropriate therapy window that has been predetermined to
support the effect and the time. In general, patient programmer 14
may initiate a clock or other timing device to track the running of
the therapy window. When the therapy window expires, patient
programmer 14 may send a command to stimulator 12 to stop delivery
of stimulation therapy. Alternatively, such a clock or timer may be
maintained within stimulator 12, such that a stop command from
patient programmer 14 is not needed. Instead, stimulator 12 may
stop delivery when a clock or timing device within the stimulator
indicates that the therapy window has expired.
Patient physiology may support shorter therapy windows in order to
further minimize desensitization of tissue in stomach 22. After
delivering electrical stimulation to stomach 22 that results in
stomach distention, stomach 22 may remain at least partially
distended for a residual recovery period of time during which the
stomach transitions from a distended state to a normal state. The
at least partial distention may be sufficient to retain a feeling
of satiety, or other sensation discouraging food intake, in patient
16 during the recovery period. In some cases, it may take stomach
22 between 30 and 60 minutes to recover from the stimulation
induced distention and return to a baseline gastric volume level.
In other words, the stomach may require 30 to 60 minutes to
decrease to a baseline volume from a 50% increased (distended)
volume induced by stimulation. Consequently, system 10 may take
advantage of this "residual" distention of stomach 22 and deliver
stimulation for a duration just long enough to effectively distend
the stomach to a desired volume and subsequently turn off the
stimulation, relying on the residual distention to effectively
treat patient 16 for a longer period of time even though
stimulation has been terminated. In this disclosure, the 50%
increase is described for purposes of illustration. However, other
increase levels or other parameters may be selected as an
indication of the desired therapeutic effect. Moreover, other types
of desired therapeutic effects, in addition or as an alternative to
distention, may be use.
After stimulation is turned off, i.e., upon expiration of the
therapy window, the distention may remain above a desired level for
a desired period of time, e.g., at or above a 50% increase in
gastric volume from a baseline gastric volume, e.g., as would be
indicated by a balloon barostat. For example, a desired therapeutic
effect may be distention that causes an increase in gastric volume
of at least 50% relative to a pre-stimulation baseline value. In
this case, 50% serves as a threshold percentage for the desired
therapeutic effect. Hence, a delay in post-stimulation recovery to
the baseline volume may permit selection of shorter therapy windows
while still maintaining desired therapeutic results beyond the
expiration of the therapy windows.
In this manner, system 10 may further limit the duration of
electrical stimulation and desensitization to the tissue adjacent
electrodes 24, 26. Again, a therapy window may be selected to
promote stimulation-induced distention of the stomach to a desired
volume effective in causing a feeling of satiety, with the
knowledge that residual, post-stimulation distention may maintain
the feeling of satiety for some time after termination of
stimulation. The appropriate length of the therapy window may be
selected based on a determination or estimation of a length, i.e.,
a first period of time, sufficient to achieve a desired therapeutic
effect for a desired period of time, i.e., a second period of
time.
The second period of time extends beyond the first period of time.
In some cases, the second period of time may be greater than the
first period of time. In other cases, the second period of time may
be less than the first period of time. The second period of time,
during which the desired therapeutic effect is maintained, may be
inclusive of the first period of time, or overlap with at least a
portion of the first period of time, during which stimulation is
delivered. The length of the first period of time defining the
therapy window may be estimated based on the length of a second
period of time in which a typical therapeutic effect is observed
for a class of patients. Alternatively, the length of the first
period of time may be determined for individual patients and
customized based on therapeutic effect measured for such
patients.
For an example therapeutic effect of gastric distention that causes
an increase in gastric volume from an initial volume, the first and
second periods of time both may be on the order of a few minutes to
a few hours. For example, the first period of time during which
stimulation is delivered may be on the order of a few minutes to
several minutes, while the second period of time, which is longer
than the first period of time, could be several minutes to a few
hours. As one illustration, the first period of time could be
approximately five minutes, while the second period of time, due to
residual effects, may be approximately 30 to 60 minutes.
Alternatively, the first period of time could be approximately one
hour while the second period of time is approximately one and
one-half hours, depending on the selected stimulation parameters
and the physiological response of the patient.
Because battery longevity in an implantable stimulator is a
paramount concern, a shorter therapy window defined by the first
period of time may also provide a significant benefit in power
reduction. Implantation of stimulator 12 in patient 16 requires
surgery. Similarly, surgery may be required for explanation of
stimulator 12 in the event battery resources are exhausted, as well
as for re-implantation of a replacement stimulator. To reduce the
number of surgical operations, and associated pain, recovery time,
and risks, it is desirable to preserve battery resources to the
extent possible while ensuring therapeutic efficacy. Because
shorter electrical stimulation durations may reduce power
consumption while increasing battery longevity, delivery of gastric
stimulation therapy in addition to utilizing the residual
distention of stomach 22 to prolong therapeutic effects may achieve
therapeutic efficacy in causing gastric distention while promoting
battery longevity. Even if a rechargeable battery is used,
application of a therapy window feature may be effective in
increasing the operating time between charges.
As discussed above, the therapy window may be selected, in some
embodiments, as a first period of time during which stimulation
must be applied in order to produce therapeutic effects for a
desired period of time. This first period of time may be selected
as approximately a minimum period of time sufficient to produce the
desired therapeutic effect for the second period of time.
Accordingly, if the desired therapeutic effect is desired for the
second period of time, then the first period of time is selected as
approximately the minimum period of time sufficient to support
maintenance of the desired therapeutic effect for the second period
of time. The first period of time may vary based on the patient and
applicable stimulation therapy parameters, such as current or
voltage amplitude, pulse rate, pulse width, electrode configuration
and the like.
It may be determined or estimated for a particular patient or class
of patients that electrical stimulation on the order of x minutes
generally produces prolonged therapeutic effects on the order of
z=x+y minutes, where y represents the number of minutes for which
therapy is deemed effective following termination of the
application of stimulation energy during the first period of time
x. If the therapeutic effect does not reach a desired level until
after stimulation has been delivered for part of the first period
of time, e.g., after m minutes, then the second period of time may
be equivalent to z-m minutes.
As an example, if the stimulation has parameters selected to cause
gastric distention, a physician or other caregiver may determine
the parameters and duration of electrical stimulation sufficient to
achieve a desired volumetric change in the stomach, as well as the
time following termination of stimulation for which the volumetric
change remains in effect or remains above a threshold percentage,
e.g., 50% above a baseline, pre-stimulation volume. The duration
found to be effective in producing the desired volumetric change
and maintaining the volumetric change or an acceptable percentage
of the volumetric change, e.g., 50%, for a desired, second period
of time may then be designated as the therapy window used as the
first period of time. The therapy window may change according to
the particular parameters applied for electrical stimulation.
Patient programmer 14 or stimulator 12 may use the therapy window
to limit the time for which stimulation is applied, while ensuring
that a prolonged therapeutic effect, such as gastric distention, is
maintained for a desired period of time after cessation of
stimulation. Hence, the maximum period of time specified by the
therapy window as the first period of time for delivery of
stimulation may be selected as the minimum period of time
sufficient to produce the desired therapeutic effect for the second
period of time, given the residual therapeutic effect that remains
following cessation of stimulation. As discussed above, the therapy
window may be estimated or determined empirically by clinical
evaluation of a particular patient, e.g., by gastric volume
analysis during and after application of stimulation for the
particular patient or a class of patient.
Hence, upon receiving a request to deliver gastric electrical
stimulation therapy, a programmer 14 or stimulator 12 may deliver
the gastric stimulation therapy for a first period of time as a
therapy window. Delivery of stimulation therapy may be requested by
a patient or requested internally within a programmer or stimulator
as an automated request, e.g., according to a therapy schedule.
Again, the first period of time may be selected as a function of an
approximate duration of the gastric electrical stimulation therapy
that is effective in producing a desired therapeutic effect for a
second period of time. The second period of time for which the
desired therapeutic effect is produced may be less than, equal to,
or greater than the first period of time. The first period of time
that is sufficient to produce the desired therapeutic effect for
the second period of time may vary according to selected
stimulation parameters and stimulation site. The second period of
time may be the overall time for which a desired therapeutic result
is achieved.
The first period of time may be greater than or equal to a minimum
time for which stimulation is delivered in order to cause the
desired therapeutic effect to last for the second period of time.
In some cases, a small time margin may be added to this minimum
time to produce the first period of time. Accordingly, the first
period of time defining the therapy window may be the minimum time
or some other time that is selected or determined based on or as a
function of the minimum time. To promote anti-desensitization and
conserve battery resources, however, it may be desirable to select
the first period of time to be approximately a minimum period of
time sufficient to produce the desired therapeutic effect for the
second period of time. Ordinarily, the first and second periods of
time may overlap. The second period of time may subsist for some
time following expiration of the first period of time. In other
words, the desired therapeutic effect for the second period of time
may last for some period of time after delivery of electrical
stimulation therapy has ceased. The first period of time limits the
duration of delivery of stimulation to the patient. The second
period of time is the time for which a desired therapeutic effect
produced by the stimulation remains in effect.
The desired therapeutic result may be a physiological response such
as a degree of gastric distention, i.e., which may correlated with
a degree of gastric relaxation. A degree of gastric distention may
be measured in terms of an increase in a gastric volume that is at
least 50% above a baseline or pre-stimulation level, i.e., a level
of gastric volume prior to application of electrical stimulation.
The 50% level is used for purposes of illustration. Other target
levels may also be specified, such as 35% or 65% above baseline
levels. For example, before gastric electrical stimulation is
applied, a baseline gastric volume may be measured with a balloon
barostat. Upon delivery of gastric stimulation, gastric volume
begins to increase to a preselected gastric volume target level of
50% above the baseline gastric volume level. Other target levels
less than or greater than 50% may be specified, as mentioned above,
depending on the needs of the patient. Upon termination of gastric
stimulation, gastric volume may slowly decay from the target level
to the initial baseline level, pre-stimulation level, or some other
level. The time during which gastric volume is at or greater than
the target level may be considered to be the second period of time
during which the desired therapeutic effect is maintained.
The amount of time that the gastric volume is above the target
level is the time during which the desired therapeutic effect is
maintained, and may be determined as follows. After insertion of a
barostat balloon into the stomach of a patient, and adjusting the
balloon pressure to a level above the abdominal pressure at time
t0, a baseline stomach volume may be determined. Upon initiating
gastric stimulation at time t1, gastric volume begins to increase,
reaching the example target level of 50% above baseline at time t2,
and the maximum volume at time t3. The target level of 50% above
baseline volume may be referred to as the therapeutic
threshold.
After delivery of gastric electrical stimulation is discontinued at
time t4, gastric volume may decline over time, decreasing to 50%
above baseline by time t5, and returning to baseline levels by time
t6. The therapy window T1 (=t4-t1) indicates the time during which
electrical stimulation is delivered. The second period of time T2
(=t5-t2) that the gastric volume remains above the therapeutic
level, i.e., producing the desired therapeutic effect, generally
extends beyond the stimulation time T1, i.e., the first period of
time or therapy window, during which stimulation is applied. The
overall second period of time T2 may be greater than or less than
the stimulation time T1.
The actual times T1 and T2 may be measured in animals or humans
using devices and techniques well known in the field of
gastroenterology, including the balloon barostat. Other techniques
or devices which assess the state of tonic muscle contraction in
the stomach may also be used to determine the first and second
periods of time T1 and T2 including those that measure changes in
length or thickness of a segment of the stomach using ultrasound,
mechanical, optical, magnetic, or other electronic transducers.
As an illustration, the result may be a therapy window that permits
delivery of stimulation within a therapy window of 5 minutes, with
a prolonged effect of 30 minutes after cessation of stimulation.
Hence, therapy may be delivered for only a first period of time T1
of approximately 5 minutes to achieve an overall desired
therapeutic effect over a second period of time T2 of approximately
35 minutes (or somewhat less than 35 minutes in the event the
desired therapeutic effect is not immediately produced upon
application of stimulation), which may be inclusive of the first
period of time or a portion of the first period of time. The second
period of time may overlap with the first period of time, but
subsist for some period of time after cessation of delivery of
stimulation. In other words, the second period of time extends at
least in part beyond an end of the first period of time. In this
manner, stimulator 12 only needs to deliver stimulation for a first
period of time T1 that is long enough to ensure a desired
therapeutic effect over a desired second period of time T2.
By delivering stimulation for a first period of time selected to
produce a therapeutic effect for a second, desired period of time,
rather than delivering stimulation for the entire desired period of
time for the therapeutic effect, a stimulator may reduce power
consumption and reduce desensitization that may result from
prolonged delivery of stimulation. The ratio of the length of the
therapy window to the length of time that the desired therapeutic
effect remains substantially intact may vary according to the type
of therapeutic effect, the patient, the stimulation parameters used
to deliver the stimulation, electrode configuration, stimulation
target site, or other factors.
As another anti-desensitization feature, patient programmer 14,
stimulator 12, or both may only permit stimulation to be delivered
according to a therapy schedule that specifies times during which
stimulation is permitted. Such times may be, for example,
approximately one to three hour windows selected at or around
ordinary meal times or snack times. For example, patient programmer
14 may be configured to permit therapy delivery during time periods
corresponding to ordinary breakfast, lunch and dinner times, as
well as snack times, if necessary. A therapy window specifying the
maximum continuous time for which stimulation may be delivered may
be placed at different temporal positions within such a time
period.
In this manner, when a patient attempts to activate stimulation,
patient programmer 14 may determine whether the activation request
is made within one of the permitted time periods on the therapy
schedule. If so, patient programmer 14 transmits a command to
stimulator 12 to cause the stimulator to deliver therapy, possibly
subject to other desensitization features, such as lockout period
and therapy window features, e.g., as described above. If the
request is not made within a permitted time period on the therapy
schedule, patient programmer 14 does not send a command to
stimulator 12 to initiate therapy, and instead may generate a
notification advising the patient 16 that therapy is not permitted
at the requested time.
As an alternative, stimulator 12 may be responsible for maintaining
the therapy schedule feature. In this case, programmer 14 may
transmit a command to start electrical stimulation therapy in
response to a patient request. If stimulator 12 receives the
command from programmer 14 within a permitted period of time on the
therapy schedule, it may deliver stimulation. Delivery of
stimulation may be subject to other anti-desensitization features
such as lockout period and therapy window. If stimulator 12
receives the command from programmer 14 at a time that is not
within a permitted period of time on the therapy schedule,
stimulator refuses to deliver stimulation and may transmit a
message notifying programmer 14 of such refusal, in which case the
programmer may generate a notification for the patient 16.
The therapy schedule may be the same every day. To further prevent
or delay desensitization, however, the therapy schedule maintained
by programmer 14 and/or stimulator 12 may be adjusted to vary the
start times for the permitted periods of time, e.g., by minutes or
hours. Hence, variation of the start time of the gastric
stimulation throughout therapy may provide another
anti-desensitization feature. When stimulation is delivered to a
specific tissue site at the same time every day, the tissue site
may become desensitized to the stimulation as the tissue becomes
accustomed to the routine stimulation. In addition, a patient 16
may adjust his behavior due to routine stimulation by ignoring the
stimulation or changing behavior around the routine stimulation
start times. Therefore, beginning stimulation at varying start
times may help to reduce desensitization.
Different start times may be used every day, week, month, or at any
time during therapy. The start times may vary by minutes or hours,
as indicated above. Variation of the stimulation start times may be
accomplished by programmer 14 or stimulator 12 by cycling through
multiple start times that have been pre-programmed by the
clinician. In other cases, stimulator 12 or programmer 14 may
randomly select a start time for each delivery of stimulation,
possibly subject to some constraints. For example, stimulator 12 or
programmer 14 may select a random start time within a preprogrammed
range or the randomized start times may be weighted around a target
start time.
In the case of weighted randomized start times, stimulator 12 may
vary start times while still starting stimulation at some time near
the target start time desired by the clinician and/or patient 16.
The weighting may be varied during therapy as well in order to
further vary start times or accommodate a changing patient
schedule. In general, it may be desirable that the therapy schedule
conform to meal and snack times. Therefore, permitted periods of
time and associated start times on the therapy schedule may vary
but still be close to meal and snack times for the patient. As an
illustration, a permitted period of therapy associated with lunch
may have a permitted start time that varies from 11:30 one day,
12:00 the next day, and 11:45 the next day. As a further measure,
stimulator 12 or programmer 14 may be configured to vary end times
of permitted periods of time during which stimulation may be
applied.
Alternatively, or additionally, multi-site stimulation may be
provided as an anti-desensitization feature to vary the location of
electrical stimulation to extend efficacious therapy of stomach 22.
Multiple electrodes may be located on stomach 22 and connected to
stimulator 12. For example, electrodes 24, 26 may be electrode
arrays in which stimulator 12 may selectively activate one or more
electrodes of the arrays during therapy to select different
electrode combinations. The electrode combinations may be
associated with different positions on the stomach or other
gastrointestinal organ. For example, the electrodes combinations
may be located at the different positions or otherwise positioned
to direct stimulation to the positions. In this manner, different
electrode combinations may be selected to deliver stimulation to
different tissue sites. The selection of electrodes forming an
electrode combination used for delivery of electrical therapy at
one time may change to a different selection of electrodes forming
an electrode combination for delivery of electrical therapy at a
different time. The selection may vary between each delivery of
stimulation or a predetermined number of delivery periods or total
amount of delivery time.
In general, to implement the multi-site feature for
anti-desensitization, a programmer or stimulator may cause delivery
of first electrical stimulation therapy to a gastrointestinal organ
of a patient via a first electrode combination associated with a
first position on the gastrointestinal organ for a first period of
time, and delivery of second electrical stimulation therapy to the
gastrointestinal organ via a second electrode combination
associated with a second position on the gastrointestinal organ for
a second period of time. The first and second electrical
stimulation therapies are configured to produce a substantially
identical therapeutic result. The different electrode combinations
may provide different stimulation channels. As an example,
stimulation delivered via the first and second channels may be
configured to produce gastric distention, nausea or discomfort to
discourage food intake by the patient. In some cases, the
stimulation may be configured to regulate gastric motility. In
other cases, the stimulation may be configured to not regulate
motility, and instead promote distention, nausea or discomfort.
A first electrode combination may include electrodes implanted at
one location on the stomach, or elsewhere in the gastrointestinal
tract, and the second electrode combination may include electrodes
implanted at a different location. In this manner, the stimulation
therapy is delivered to two or more different tissue sites. The
first and second electrode combinations may be implanted in the
same gastrointestinal organ. For example, the first and second
electrode combinations may both be implanted in the stomach, or may
both be implanted in the intestine. Each electrode combination may
comprise two or more electrodes, which may be provided on one or
more implantable leads. In some cases, an electrode combination may
include the device housing or can as an electrode.
Each of first and second periods of time may be greater than or
equal to approximately 30 seconds, greater than or equal to one
minute, greater than or equal to five minutes, greater than or
equal to ten minutes, greater than or equal to one hour, or greater
than or equal to one day. The first and second periods of time may
partially overlap or not overlap with one another. The first and
second periods of time for which stimulation is delivered to first
and second electrode combinations, respectively, may be equal to or
different from one another. In general, the first and second
periods of time will not be coextensive.
By delivering stimulation to different electrode combinations at
different tissue sites at different times, desensitization of one
tissue site may be reduced. As the first and second periods of time
are lengthened, however, a single tissue site may be exposed to
stimulation for an extended period of time. Accordingly, shorter
periods of time on the order of seconds, minutes, hours or days may
be desirable, e.g., in contrast to weeks or months. Over the
potentially lengthy operational life of a stimulator, however,
delivering stimulation via one electrode combination for weeks or
months followed by switching delivery to a second electrode
combination for weeks or months may still be desirable.
When the selection of electrode combination is changed, e.g., from
the first period of time to a second period of time, patient
programmer 14 or stimulator 12 may determine the next selection of
electrodes based upon instructions defined by a clinician. The
instructions may direct the selection to progressively move to the
next set of electrodes in an electrode array, move to the next
electrodes that retain the desired distance or orientation between
electrodes, or randomly select the next electrodes to use for
delivery of therapy. In the case of randomized selection of
electrodes, a new selection may be different than the previous
selection to avoid continued electrical stimulation exposure to the
same tissues. Stimulator 12 and/or patient programmer 14 may store
each selection of electrodes used during the course of gastric
stimulation therapy so that a clinician may review the selections
and identify any potential problems with the changing electrodes or
ineffective therapy with one or more electrodes being used.
In some cases, a multi-site stimulation feature may make use of
three or more electrode combinations. For example, a programmer or
stimulator may further cause delivery of third electrical
stimulation therapy to the gastrointestinal organ via a third
electrode combination associated with a third position on the
gastrointestinal organ at a third time, repeat the delivery of the
first, second and third electrical stimulation therapies for the
first, second and third periods of time, and select an order of the
first, second and third periods of time in a varying order for at
least some of the repeated deliveries. For example, in some cases,
stimulation via the first, second, and third electrode combinations
may proceed in that order. Alternatively, stimulation could proceed
from first, to third, to second electrode combination, from third,
to second, to first electrode combination, from third, to first, to
second electrode combination, or in other orders. The first, second
and third electrical stimulation therapies may be configured to
produce a substantially identical therapeutic result. In some
cases, the first, second and third positions are arranged such that
the first position is most proximal on the gastrointestinal organ,
the third position is most distal on the gastrointestinal organ,
and the second position is between the first and third positions,
where proximal refers to portions closer to the start of the
gastrointestinal tract and distal refers to portions closer to the
end of the gastrointestinal tract.
For example, first and second electrode sets used to form first and
second electrode combinations, respectively, may be displaced from
one another by at least approximately 1 cm, more preferably at
least approximately 3 cm, and still more preferably at least
approximately 5 cm. In some cases, the electrode combinations may
be associated with positions that are greater than 10 cm apart. As
an illustration, the different electrode sets could each be
implanted within the lesser curvature of the stomach, but displaced
approximately 5 cm from one another. In this manner, the different
electrode combinations are positioned to deliver stimulation to
different tissue sites, and thereby delay or reduce likelihood of
desensitization of a given tissue stimulation site. In general,
first and second electrode sets may be implanted a sufficient
distance away from one another such that they tend to activate
different tissue sites, or otherwise be implanted to deliver
stimulation to tissue sites that are positioned a sufficient
distance away from one another. The first and second electrode
combinations may be placed at different positions on the same
organ, such as different positions on the stomach or different
positions on the small intestine. Alternatively, or additionally,
the first and second electrode combinations may be placed at
different positions on different organs, e.g., at one position on
the stomach and another position on the small intestine.
Stimulator 12 and/or programmer 14 may control the stimulator to
deliver stimulation via two or more different electrode
combinations on a time-interleaved or time-independent basis. For
example, stimulation may be delivered via different electrode
combinations on a time-interleaved basis in different time slots,
e.g., within a given therapy window or period of time on the
therapy schedule. In this case, two or more stimulation channels
may be active and controlled to deliver stimulation in respective
time slots, which may partially overlap or not overlap. In this
case, stimulation at different electrode combinations may be
delivered together within a therapy window, but on a
time-interleaved basis. Alternatively, stimulation may be delivered
via different electrode combinations in separate therapy windows,
such that each electrode combination is used separately and
independently of one another. In this case, only one channel may be
active at a time and may not coordinate timing with another channel
within a given therapy window.
As described above, stimulator 12 may include a first channel
coupled to a first set of electrodes forming a first electrode
combination and a second channel coupled to a second set of
electrodes forming a second electrode combination. Additional
channels, such as a third channel coupled to a third set of
electrodes, may be provided in some embodiments. Individual
electrodes in the sets of electrodes may be selected to form
electrode combinations, either among the electrodes or among one or
more electrodes and an electrode surface on a housing of the
stimulator. Stimulator 12 may be configured to deliver stimulation
with identical, similar or different parameters via the first and
second channels to achieve a substantially identical therapeutic
effect.
As another anti-desensitization feature, programmer 14 and/or
stimulator may apply a burst pattern parameter selection feature to
vary the characteristics of stimulation delivered to patient 16.
For example, the burst pattern parameter selection feature may
include varying stimulation parameters of pulses within bursts of
pulses delivered to patient 16. In one example, the stimulation
parameters may be varied between at least two pulses within a
single burst of pulses. Therefore, not all the pulses within a
given burst have the same stimulation parameters. In another case,
the stimulation parameters may be varied between the pulses of
successive bursts of pulses. This variation of stimulation
parameters allows for each burst to have identical pulses while the
pulses of subsequent bursts may be different. Additionally, the
parameter selection feature may specify that a combination of
pulses are varied within a burst and between subsequent bursts.
As a further alternative, pulses may be delivered in burst
patterns, where each pattern contains multiple pulse bursts. In
this case, pulse parameters may be varied among different burst
patterns. For example, first pulses in bursts associated with a
first burst pattern may have identical pulse parameters, while
second pulses in bursts associated with a second burst pattern may
have one or more pulse parameters that are different from pulse
parameters associated with the first pulses in the first burst
pattern. Hence, successive burst patterns may have one or more
different pulse parameters. Alternatively, pulses within bursts in
a first burst pattern may be varied relative to one another, and
relative to pulses within bursts in a second burst pattern. In
addition, timing of bursts in different burst patterns may be
varied.
The variation of stimulation parameters between pulses may be of
slight magnitude so that the stimulation pulses are not constantly
the same without drastically changing the efficacy of the
stimulation therapy as a whole. In other words, the variation in
stimulation parameters may be only directed to have an effect upon
the desensitization of the tissue and not the overall effect of the
perceived therapy. For example, a stimulation parameter change from
a previous pulse to a subsequent pulse may differ by less than
approximately ten percent, or less than approximately five percent.
However, the stimulation parameters may change by more than
approximately ten percent in some cases where stimulation efficacy
is not affected by the larger magnitude changes.
The stimulation parameters that may be varied for the
desensitization measure may be current amplitude, voltage
amplitude, pulse width, pulse rate, and/or duty cycle. One or more
stimulation parameters may be varied at any given time, as long as
the stimulation therapy remains effective in treating patient 16.
The progression of variation of the stimulation parameter changed
to prevent tissue desensitization may be selected by the clinician
during therapy programming. The stimulation parameter may cycle
between preset parameter values specified by the clinician, vary
randomly between a minimum limit and a maximum limit, vary with a
weighted randomization that is centered to a target or programmed
parameter value, or vary in some other way specified by the
clinician. In any case, stimulator 12 may implement an
anti-desensitization feature that varies the stimulation parameters
over the course of therapy in order to extend the efficacy of
gastric stimulation therapy.
System 10 may implement more than one anti-desensitization feature
at any given time. For example, system 10 may implement the lockout
period after the therapy window has elapsed. In addition, the
lockout period and therapy window may be subject to the therapy
schedule, and vice versa. In another example, system 10 may
implement the lockout period in addition to ordered, randomized, or
pseudo-randomized selection of electrodes to vary the location of
electrical stimulation periodically throughout therapy. In any
case, the anti-desensitization feature used by system 10 may be
effective in extending therapy efficacy by reducing or preventing
tissue desensitization that shortens the useful life of electrical
stimulation therapy. The term "pseudo-random" may generally refer
to a quasi random or effectively random output generated by a
system, such as software running on a microprocessor (e.g., random
number generators), and may be limited to a predetermined range of
values.
Stimulator 12 delivers electrical stimulation according to
stimulation parameters stored within stimulator 12. In one example,
stimulator 12 delivers stimulation pulses with a pulse width
selected to promote gastric distention and/or modulate gastric
motility. A pulse width in a range of approximately 1 milliseconds
to approximately 50 milliseconds, more preferably in a range of
approximately 1.5 milliseconds to approximately 10 milliseconds,
more preferably approximately 2 milliseconds to approximately 10
milliseconds, and even more preferably approximately 2 to 5
milliseconds, may be effective in causing gastric distention while
promoting better power conservation. As an example, the stimulation
pulses delivered by stimulator 12 may have a pulse width greater
than or equal to approximately 1 millisecond (ms), but generally
less than approximately 10 ms. More specifically, the pulse width
may be between approximately 2 ms and 5 ms. Pulse widths in this
range may be long enough to promote gastric distension but short
enough that patient 16 does not generally perceive significant
negative effects from the stimulation, e.g., nausea, or cause
excessive power consumption.
In another example, stimulator 12 may be programmed to produce
feelings of nausea to limit the desire of patient 16 to eat. In
this case, pulse widths may be generally greater than approximately
0.5 ms and as long as approximately 50 ms. In still another
example, stimulator 12 may deliver pulses with a pulse width
greater than approximately 2 ms to reduce motility. In this case,
the pulse width may be between approximately 1 ms and approximately
100 ms. Other pulse widths may be used for additional therapy
outcomes. The clinician may program the stimulation parameters,
such as the pulse width, amplitude, pulse rate, electrode
combinations and polarities, upon implant of stimulator 12 and
possibly in subsequent clinic visits, in order to appropriately
treat the condition of patient 16.
With further reference to FIG. 1, at the outer surface of stomach
22, e.g., along the lesser curvature 23, leads 18, 20 penetrate
into tissue such that electrodes 24 and 26 are positioned to
deliver stimulation to stomach 22. As mentioned above, the
parameters of the stimulation pulses generated by stimulator 12 may
be selected to distend stomach 22 and thereby induce a sensation of
fullness, i.e., satiety. In some embodiments, the parameters of the
stimulation pulses also may be selected to induce a sensation of
nausea. In each case, the induced sensation of satiety and/or
nausea may reduce a patient's desire to consume large portions of
food. Alternatively, the parameters may be selected to regulate
motility, e.g., for gastroparesis. Again, the stimulation pulses
may be delivered elsewhere within the gastrointestinal tract,
either as an alternative to stimulation of lesser curvature 23 of
stomach 22, or in conjunction with stimulation of the lesser
curvature of the stomach. As one example, stimulation pulses could
be delivered to the greater curvature of stomach 22 located
opposite lesser curvature 23.
For obesity therapy, the pulse width and/or other parameters may be
selected so that electrical stimulation, when applied, causes at
least approximately a twenty-five percent increase in gastric
volume relative to a baseline gastric volume, preferably at least
approximately a thirty-five percent increase in gastric volume,
more preferably at least approximately fifty percent increase in
gastric volume, more preferably at least approximately a sixty-five
percent increase in gastric volume, more preferably at least
approximately a seventy-five percent increase in gastric volume,
and still more preferably at least approximately a one-hundred
percent increase in gastric volume. The increase in gastric volume
may be measured relative to a baseline gastric volume, such as a
preprandial (pre-meal) and/or pre-stimulation gastric volume, and
may be measured within a selected area of the gastrointestinal
tract. For example, the gastric volume may be measured within the
stomach if electrical stimulation is applied to the stomach.
Alternatively, the baseline and stimulation-induced gastric volume
may be measured elsewhere within the gastrointestinal tract if
electrical stimulation is applied elsewhere.
In addition to pulse width, the stimulation pulses are defined by
other parameters including current or voltage amplitude, pulse
rate, and duty cycle. In some embodiments, stimulation parameters
may further include electrode combinations and polarities in the
event leads 18, 20 provide multiple electrode positions. As an
illustration, in addition to a pulse width in the ranges identified
above, stimulator 12 may generate stimulation pulses having a
current amplitude in a range of approximately 1 to 20 milliamps
(mA), preferably approximately 2 to 10 mA, and more preferably
approximately 3 to 6 mA. An example voltage may be between
approximately 0.5 volts and 10 volts. The pulse rate of the
stimulation pulses may be in a range of approximately 0.05 to 50
Hertz (Hz), preferably approximately 1 to 50 Hz, more preferably
approximately 10 to 50 Hz, and more preferably approximately 20 to
50 Hz. As an illustration, a substantial amount of distention may
be produced with a pulse width of approximately 2 ms in combination
with a pulse rate of approximately 40 Hz.
In addition, in some embodiments, stimulator 12 may deliver
stimulation pulses with a duty cycle of approximately 50% ON/50%
OFF, preferably 30% ON/70% OFF, and more preferably 20% ON/80% OFF.
The pulses may be generated in bursts, and the bursts may be
generated in burst patterns containing multiple bursts. Duty cycle
generally refers to the percentage of time that stimulator 12 is
delivering stimulation pulses versus the percentage of time during
which the stimulator is idle, i.e., not delivering pulses. During
ON time, stimulator 12 delivers pulses according to a set of
parameters such as amplitude, pulse rate and pulse width. During
OFF time, stimulator 12 does not deliver stimulation pulses to
patient 16.
In addition, the duty cycle may include the amount of time
stimulation pulses are delivered and the amount of time pulses are
not delivered to patient 16 when the stimulator 12 is ON.
Additionally, a higher level duty cycle includes the amount of time
stimulator 12 is ON and OFF. In this manner, example stimulation
therapy may have duty cycles that describe when stimulator 12 is ON
and OFF in addition to cycles that describe the amount of time
pulses are delivered to patient 16 during the ON period. Stimulator
12 may also have nested duty cycles, such as can be defined as
bursts of pulses during an ON period of stimulation. Bursts of
pulses and burst patterns will be further discussed below.
As one illustration, to cause gastric distention, stimulator 12 may
deliver stimulation pulses with an amplitude of approximately 1 to
10 mA, a pulse width of approximately 2 to 10 milliseconds (ms), a
pulse rate of approximately 1 to 60 Hz, and a duty cycle of
approximately 25% ON/75% OFF. As another illustration, stimulator
12 may deliver stimulation pulses with an amplitude of
approximately 3 to 6 mA, a pulse width of approximately 2 to 5
milliseconds (ms), a pulse rate of approximately 20 to 50 Hz, and a
duty cycle of approximately 40% ON/60% OFF. Such pulses may be
delivered as bursts or burst patterns containing multiple bursts.
In each case, stimulator 12 may cause substantial gastric
distention and a sensation of fullness, which may result in reduced
food intake and, ultimately, weight loss.
Implantable stimulator 12 may be constructed with a biocompatible
housing, such as titanium, stainless steel, or a polymeric
material, and is surgically implanted within patient 16. The
implantation site may be a subcutaneous location in the side of the
lower abdomen or the side of the lower back. Stimulator 12 is
housed within the biocompatible housing, and includes components
suitable for generation of electrical stimulation pulses.
Stimulator 12 may be responsive to patient programmer 14, which
generates control signals to adjust stimulation parameters. As a
further embodiment, stimulator 12 may be formed as an RF-coupled
system in which an external controller such as patient programmer
14 or another device provides both control signals and inductively
coupled power to an implanted pulse generator.
Electrical leads 18 and 20 are flexible and include one or more
internal conductors that are electrically insulated from body
tissues and terminated with respective electrodes 24 and 26 at the
distal ends of the respective leads. The leads may be surgically or
percutaneously tunneled to stimulation sites on stomach 22. The
proximal ends of leads 18 and 20 are electrically coupled to the
pulse generator of stimulator 12 via internal conductors to conduct
the stimulation pulses to stomach 22 via electrodes 24, 26.
Leads 18, 20 may be placed into the muscle layer or layers of
stomach 22 via an open surgical procedure, or by laparoscopic
surgery. Leads also may be placed in the mucosa or submucosa by
endoscopic techniques or by an open surgical procedure. Electrodes
24, 26 may form a bipolar pair of electrodes. Alternatively,
stimulator 12 may carry a reference electrode to form an "active
can" arrangement, in which one or both of electrodes 24, 26 are
unipolar electrodes referenced to the electrode on the pulse
generator. The housing of implantable stimulator 12 may itself
serve as a reference electrode for the active can arrangement. A
variety of polarities and electrode arrangements may be used. Each
lead 18, may carry a single electrode or an electrode array of
multiple electrodes, permitting selection of different electrode
combinations, including different electrodes in a given electrode
array, and selection of different polarities among the leads for
delivery of stimulation.
In addition to pulse width, as discussed above, the stimulation
pulses delivered by implantable stimulator 12 are characterized by
other stimulation parameters such as a voltage or current amplitude
and pulse rate. Pulse width and the other stimulation parameters
may be fixed, adjusted in response to sensed physiological
conditions within or near stomach 22, or adjusted in response to
patient or physician input entered via patient programmer 14. For
example, in some embodiments, patient 16 may be permitted to adjust
stimulation amplitude, pulse width, or pulse rate and turn
stimulation ON and OFF via patient programmer 14.
Patient programmer 14 transmits instructions to stimulator 12 via
wireless telemetry. Accordingly, stimulator 12 includes telemetry
interface electronics to communicate with patient programmer 14.
Patient programmer 14 may be a small, battery-powered, portable
device that accompanies patient 16 throughout a daily routine.
Patient programmer 14 may have a simple user interface, such as a
button or keypad, and a display or lights. Patient programmer also
may include any of a variety of audible, visual, graphical or
tactile output media. Patient programmer 14 may be a hand-held
device configured to permit activation of stimulation and
adjustment of stimulation parameters.
Alternatively, patient programmer 14 may form part of a larger
device including a more complete set of programming features
including complete parameter modifications, firmware upgrades, data
recovery, or battery recharging in the event stimulator 12 includes
a rechargeable battery. Patient programmer 14 may be a patient
programmer, a physician programmer, or a patient monitor. In some
embodiments, patient programmer 14 may be a general purpose device
such as a cellular telephone, a wristwatch, a personal digital
assistant (PDA), or a pager.
Electrodes 24, 26 carried at the distal ends of lead 18, 20,
respectively, may be attached to the wall of stomach 22 in a
variety of ways. For example, the electrode may be formed as a
gastric electrode that is surgically sutured onto the outer wall of
stomach 22 or fixed by penetration of anchoring devices, such as
hooks, needles, barbs or helical structures, within the tissue of
stomach 22. Also, surgical adhesives may be used to attach the
electrodes. In some cases, the electrodes 24, 26 may be placed in
the lesser curvature 23 on the serosal surface of stomach 22,
within the muscle wall of the stomach, or within the mucosal or
submucosal region of the stomach. Alternatively, or additionally,
electrodes 24, 26 may be placed in the greater curvature of stomach
22 such that stimulation is delivered to the greater curvature.
In some embodiments, system 10 may include multiple stimulators 12
or multiple leads 18, 20 to stimulate a variety of regions of
stomach 22. Stimulation delivered by the multiple stimulators may
be coordinated in a synchronized manner, or performed without
communication between stimulators. Also, the electrodes may be
located in a variety of sites on the stomach, or elsewhere in the
gastrointestinal tract, dependent on the particular therapy or the
condition of patient 16. Stimulation delivered by the multiple
stimulators may be coordinated in a synchronized manner, or
performed independently without communication between stimulators.
As an example, one stimulator may control other stimulators by
wireless telemetry, all stimulators may be controlled by patient
programmer 14, or the stimulators may act autonomously subject to
parameter adjustment or downloads from patient programmer 14.
FIG. 2 is a block diagram illustrating example components of a
stimulator 12 that delivers gastric stimulation therapy to patient
16. In the example of FIG. 2, stimulator 12 includes stimulation
generator 28, processor 30, memory 32, wireless telemetry interface
34 and power source 36. In some embodiments, stimulator 12 may
generally conform to the Medtronic Itrel 3 Neurostimulator,
manufactured and marketed by Medtronic, Inc., of Minneapolis, Minn.
However, the structure, design, and functionality of stimulator 12
may be subject to wide variation without departing from the scope
of the disclosure as broadly embodied and described in this
disclosure.
Processor 30 controls stimulation generator 28 by setting and
adjusting stimulation parameters such as pulse amplitude, pulse
rate, pulse width and duty cycle, in the case that stimulation
generator 28 generates pulses. Alternative embodiments may direct
stimulation generator 28 to generate continuous electrical signals,
e.g., a sine wave. Processor 30 may be responsive to parameter
adjustments or parameter sets received from patient programmer 14
via telemetry interface 34. Hence, patient programmer 14 may
program stimulator 12 with different sets of operating parameters.
In some embodiments, stimulation generator 28 may include a switch
matrix. Processor 30 may control the switch matrix to selectively
deliver stimulation pulses from stimulation generator 28 to
different electrodes 38 carried by one or more leads 18, 20 (FIG.
1). In some embodiments, stimulator 12 may deliver different
stimulation programs to patient 16 on a time-interleaved basis with
one another.
Memory 32 stores instructions for execution by processor 30,
including operational commands and programmable parameter settings.
Example storage areas of memory 32 may include instructions
associated with therapy programs 33 and anti-desensitization
features 35. Programs 33 may include each program used by
stimulator 12 to define parameters and electrode combinations for
gastric stimulation therapy. Anti-desensitization features 35 may
include instructions for application of one or more
anti-desensitization features, as described in this disclosure,
such as when to start and stop a lockout period, therapy window
durations, therapy schedules, burst pattern variation parameters,
multi-site stimulation parameters, electrode selection orders or
functions, and burst pattern parameter selection instructions.
Processor 30 may access a clock or other timing device 29 within
stimulator 12 to determine pertinent times, e.g., for enforcement
of therapy schedules, lockout periods, and therapy windows, and may
synchronize such times with times maintained by patient programmer
14. Memory 32 may include one or more memory modules constructed,
e.g., as random access memory (RAM), read-only memory (ROM),
non-volatile random access memory (NVRAM), electrically erasable
programmable read-only memory (EEPROM), and/or FLASH memory.
Processor 30 may access memory 32 to retrieve instructions for
control of stimulation generator 28 and telemetry interface 34, and
may store information in memory 32, such as operational
information.
Wireless telemetry in stimulator 12 may be accomplished by radio
frequency (RF) communication or proximal inductive interaction of
implantable stimulator 12 with patient programmer 14 via telemetry
interface 34. Processor 30 controls telemetry interface 34 to
exchange information with patient programmer 14. Processor 30 may
transmit operational information and receive stimulation parameter
adjustments or parameter sets via telemetry interface 34. Also, in
some embodiments, stimulator 12 may communicate with other
implanted devices, such as stimulators or sensors, via telemetry
interface 34.
Power source 36 delivers operating power to the components of
implantable stimulator 12. Power source 36 may include a battery
and a power generation circuit to produce the operating power. In
some embodiments, the battery may be rechargeable to allow extended
operation. Recharging may be accomplished through proximal
inductive interaction between an external charger and an inductive
charging coil within implantable stimulator 12. In other
embodiments, an external inductive power supply may
transcutaneously power implantable stimulator 12 whenever
stimulation therapy is to occur.
Implantable stimulator 12 is coupled to electrodes 38, which may
correspond to electrodes 24 and 26 illustrated in FIG. 1, via one
or more leads 18, 20. Implantable stimulator 12 provides
stimulation therapy to the gastrointestinal tract of patient 16.
Stimulation generator 28 includes suitable signal generation
circuitry for generating a voltage or current waveform with a
selected amplitude, pulse width, pulse rate, and duty cycle. In
general, as described in this disclosure, the electrical
stimulation and stimulation pulses generated by stimulation
generator 28 may be formulated with pulse widths and appropriate
times suitable to cause substantial gastric distention without
excessive consumption of power provided by power source 36.
In the example of FIGS. 1 and 2, stimulator 12 includes leads 18,
20. In other embodiments, stimulator 12 may be a leadless
stimulator, sometimes referred to as a microstimulator, or
combination of such stimulators. In this case, the housing of
stimulator 12 may include multiple electrodes to form electrode
combinations for delivery of stimulation to the stomach,
intestines, or other organs within patient 16. In additional
embodiments, stimulator 12 may include three of more leads.
FIG. 3 is a block diagram illustrating example components of
patient programmer 14 that receives patient input and communicates
with stimulator 12. As shown in FIG. 3, patient programmer is an
external programmer that patient 16 uses to control the gastric
stimulation therapy delivered by stimulator 12. Patient programmer
14 includes processor 40, user interface 42, memory 44, telemetry
interface 50 and power source 52. In addition, processor 40 may
access a clock or other timing device 41 to adhere to lockout
periods, therapy windows, and therapy schedules, as applicable.
Patient 16 may carry patient programmer 14 throughout therapy so
that the patient can initiate, stop and/or adjust stimulation as
needed.
While patient programmer 14 may be any type of computing device,
the patient programmer may preferably be a hand-held device with a
display and input mechanism associated with user interface 42 to
allow interaction between patient 16 and patient programmer 14.
Patient programmer 14 may be similar to a clinician programmer used
by a clinician to program stimulator 12. The clinician programmer
may differ from patient programmer by having additional features
not offered to patient 16 for security, performance, or complexity
reasons.
User interface 42 may include display and keypad (not shown), and
may also include a touch screen or peripheral pointing devices.
User interface 42 may be designed to receive an indication from
patient 16 to deliver gastric stimulation therapy. The indication
may be in the form of a patient input in the form of pressing a
button representing the start of therapy or selecting an icon from
a touch screen, for example. In alternative examples, user
interface 42 may receive an audio cue from patient 16, e.g., the
patient speaks to a microphone in order to perform functions such
as beginning stimulation therapy. Patient programmer 14 acts as an
intermediary for patient 16 to communicate with stimulator 12 for
the duration of therapy.
User interface 42 may provide patient 16 with information
pertaining, for example, to the status of an indication or a
gastric stimulation function. Upon receiving the indication to
start stimulation, user interface 42 may present a confirmation
message to patient 16 that indicates stimulation has begun. The
confirmation message may be a picture, icon, text message, sound,
vibration, or other indication that communicates the therapy status
to patient 16. User interface 42 also may provide the status of an
anti-desensitization feature to patient 16. For example, user
interface 42 may indicate that the lockout period is currently
active, e.g., with a small lock symbol displayed on the screen, or
that a therapy window is about to expire.
In addition, user interface 42 may present information relating to
the therapy schedule or therapy windows. In some cases, user
interface 42 may prompt the patient 16 to initiate stimulation when
a permitted time period on the therapy schedule has arrived.
Alternatively, user interface 42 may display a lockout message pop
up window to patient 16 if the user interface receives an
indication from patient 16 to deliver therapy during the lockout
period. In any case, user interface 42 may notify patient 16 when
request indicated by patient input has been completed or cannot be
completed due to a restriction.
Processor 40 may include one or more processors such as a
microprocessor, a controller, a DSP, an ASIC, an FPGA, discrete
logic circuitry, or the like. Processor 40 may control information
displayed on user interface 42 and perform certain functions when
requested by patient 16 via input to the user interface. Processor
40 may retrieve data from and/or store data in memory 44 in order
to perform the functions of patient programmer 14 described herein.
For example, processor 40 may generate a selection of electrodes as
an anti-desensitization feature based upon instructions stored in
memory 44, and processor 40 may then store the selection in memory
44.
Memory 44 may include programs 46 that are stimulation programs
used to define therapy delivered to patient 16. When a new program
is requested by stimulator 12 or patient 16, one of programs 46 may
be retrieved from memory 44 and transmitted to stimulator 12 in
order adjust the gastric stimulation therapy. Alternatively,
patient 16 may generate a new program during therapy and store it
with programs 46. Memory 44 may store instructions relating to
anti-desensitization features 48, which may include instructions
relating to the lockout period, therapy window, therapy schedule,
burst pattern parameter selection, a burst pattern variation,
and/or multi-site features. For the lockout period, for example,
such instructions may define the duration of the lockout period,
when to start and stop the lockout period, or any other parameters
that may define the lockout period. Memory 44 may include any
volatile, non-volatile, fixed, removable, magnetic, optical, or
electrical media, such as a RAM, ROM, CD-ROM, hard disk, removable
magnetic disk, memory cards or sticks, NVRAM, EEPROM, flash memory,
and the like.
While patient programmer 14 is generally described as a hand-held
computing device, the patient programmer may be a notebook
computer, a cell phone, or a workstation, for example. In some
embodiments, patient programmer 14 may comprise two or more
separate devices that perform the functions ascribed to the patient
programmer. For example, patient 16 may carry a key fob that is
only used to start or stop stimulation therapy. The key fob may
then be connected to a larger computing device having a screen via
a wired or wireless connection when information between the two
needs to be synchronized. Alternatively, patient programmer 14 may
simply be small device having one button, e.g., a single "start"
button, that only allows patient 16 to start stimulation therapy
when the patient feels hungry or is about to eat.
Stimulator 12 may store and implement any of the
anti-desensitization features, such as the lockout period, the
therapy window, and the selection of electrodes. When patient 16
presses the single start button to start stimulation again, the
stimulation delivery may be subject to the anti-desensitization
features, such as the lockout period, therapy window, and/or
therapy schedule. In addition, in applying stimulation, programmer
14 and/or stimulator 12 may apply other anti-desensitization
features, such as the burst pattern parameter selection,
multi-site, and/or burst pattern variation features. Hence, in some
embodiments, programmer 14 may have only a single start button that
is accessible to the patient to attempt to activate stimulation,
subject to one or more applicable anti-desensitization features
that may control when or how stimulation is applied.
FIG. 4 is a conceptual diagram illustrating example electrode
arrays 54 and 56 positioned on stomach 22 of patent 16. As shown in
FIG. 4, electrode arrays 54 and 56 are attached to the outside of
stomach 22. Electrode array 54 includes five discrete electrodes
54A, 54B, 54C, 54D and 54E (collectively "electrodes 54") and
electrode array 56 includes five discrete electrodes 56A, 56B, 56C,
56D and 56E (collectively "electrodes 56"). Electrode arrays 54 and
56 are positioned along lesser curvature 23 of stomach 22, but the
electrode arrays may be positioned anywhere upon stomach 22 as
desired by the clinician. In addition, one or both electrode arrays
54 may be positioned at different sites, such as on the duodenum or
elsewhere along the small intestine.
Electrode arrays 54 and 56 are provided in place of electrodes 24
and 26 of FIG. 1. In this manner, electrode arrays 54 and 56 may be
used as part of a multi-site anti-desensitization feature to
distribute electrical stimulation energy among a larger number of
varied tissue sites, instead of concentrating stimulation at a
single tissue site over an extended period of time. For example,
electrode arrays 54, 56 may be used to support selection of
different electrode combinations associated with different
positions, or tissue sites, on a gastrointestinal organ such as the
stomach. Each electrode array 54, 56 may include a plurality of
electrodes, e.g., electrodes 54A-54E and electrodes 56A-56E, that
may be individually selected to form a variety of electrode
combinations that distribute electrical stimulation therapy to
different therapy sites. Electrode combinations may include
selected electrodes on different leads or the same lead. For
example, an electrode combination may combine electrodes from array
54, array 56, or both array 54 and 56, as well as electrodes from
other arrays, if provided. In general, electrodes in arrays 54, 54
may be positioned to form electrode combinations at tissue sites
separated by greater than approximately 1 cm, greater than
approximately 3 cm, or greater than approximately 5 cm. The
distribution of stimulation among electrode combinations at
different tissue sites may help to reduce desensitization and
thereby extend the efficacy of electrical stimulation without
compromising patient treatment.
In the example of FIG. 4, electrode arrays 54 and 56 and electrodes
54A-54E and 56A-56E may not necessarily be sized in proportion to
stomach 22. For example, electrode arrays 54 and 56 may be
configured to be a smaller size so that the electrodes can be
packed into a smaller area of stomach 22. Alternatively, electrode
arrays 54 and 56 and their corresponding electrodes may differ in
size on stomach 22. For example, electrodes in array 54 may each
have a larger surface area than each of the electrodes in array 56.
In addition, electrodes 54 may have differing surface areas between
each of the electrodes. In this manner, varying electrode surface
area may act as an additional anti-desensitization feature to
slightly alter the stimulation therapy over time.
Stimulator 12 may deliver electrical stimulation to stomach 22
using one or more electrodes of electrode arrays 54 and 56. Each of
the electrodes in arrays 54, 56 may be coupled to stimulator 12 via
a respective electrical conductor within leads 18, 20, and may be
individually selectable. Each lead 18, 20 may include multiple
conductors, each of which is coupled at a distal end to one of the
electrodes in a respective electrode array 54, 56 and at the
proximal end to a terminal of a switch device by which stimulator
12 directs stimulation energy to selected electrodes, e.g., as
anodes or cathodes. In some examples, as mentioned above,
stimulator 12 may deliver stimulation using one electrode from each
of electrode arrays 54 and 56, multiple electrodes from one array
and a single electrode from another array, or multiple electrodes
in a single array.
Stimulator 12 may cycle through or randomly select different
electrodes from each of electrode arrays 54 and 56 to produce
different electrode combinations to vary the stimulation tissue
sites throughout therapy. In other examples, stimulator 12 may
deliver stimulation using a combination of any electrodes from only
electrode array 54, only electrode array 56, or a combination of
electrodes from electrode arrays 54 and 56. In alternative
examples, the housing of stimulator 12 may also be used as an
electrode. The housing of stimulator 12 may be referred to as a can
electrode, return electrode, or active can electrode, as mentioned
above.
While electrode arrays 54 and 56 are shown as each having five
electrodes, electrode arrays 54 and 56 may have any number of
electrodes desired by the clinician or necessary for efficacious
therapy. Electrode arrays 54 and 56 may have differing numbers of
electrodes, and stimulator 12 may be connected to a different
number of electrode arrays, such as only one array or more than
three arrays. In addition, electrode arrays 54 and 56 may have
corresponding electrodes configured in a different orientation than
the linear orientation shown in FIG. 4. For example, electrode
arrays 54 and 56 may have electrodes oriented in a circular
pattern, rectangular grid pattern, curved pattern, star pattern, or
another pattern that may enhance the anti-desensitization feature
of electrode arrays 54 and 56.
At some time during therapy, it is possible that one or more of
electrodes 54 and 56 may no longer be functional due to a broken
lead, broken conductor, disconnected circuit, corroded electrode,
or some other problem. Stimulator 12 may recognize a dysfunctional
electrode during an electrode integrity check at various times
during therapy. Once an electrode is determined to be
dysfunctional, stimulator 12 may remove that electrode from the
possible electrodes for therapy. Stimulator 12 may also alter the
algorithm used for generating a selection of electrodes for
delivering therapy to ensure that only functional electrodes are
included in the selection. In some examples, the clinician may
manually alter the selection of electrodes when an electrode is
determined to be dysfunctional.
In general, multiple electrodes implanted at multiple tissue sites,
as shown in FIG. 4, may permit stimulation to be delivered to
different stimulation sites at different times. For example,
stimulation having substantially similar parameters or different
parameters may be applied to different tissue sites during
different therapy windows or therapy schedule time periods such
that different tissue sites are stimulated to prevent or delay
desensitization. The stimulation parameters may be selected to
achieve similar therapeutic effects, e.g., gastric distention, even
though the stimulating is delivered to different tissue sites.
Also, in some embodiments, stimulation may be delivered to
different stimulation sites during the same therapy schedule
periods or therapy windows. For example, therapy can be adjusted
during the course of stimulation to use different electrode
combinations and associated tissue sites. In addition, in other
embodiments, a multi-site feature may be applied such that
stimulation is delivered simultaneously or on an alternating,
time-interleaved basis, e.g., pulse by pulse or burst by burst or
burst pattern by burst pattern, to different electrode combinations
and different associated tissue sites.
With reference to FIG. 4, for example, one pulse or burst could be
applied to an electrode combination via array 54 while the next
pulse or burst or burst pattern could be applied to an electrode
combination via array 56. In this manner, a single tissue site is
stimulated less often. Yet, the stimulation delivered to different
tissue sites on an alternating basis may still achieve a
substantially identical desired overall therapeutic effect, e.g.,
gastric distention, nausea or discomfort in the case of
obesity.
Stimulator 12 may deliver first electrical stimulation therapy via
a first electrode combination associated with a first position on
the gastrointestinal organ for a first period of time, and deliver
second electrical stimulation therapy to the gastrointestinal organ
via a second electrode combination associated with a second
position on the gastrointestinal organ for a second period of time.
The stimulation therapies may comprises pulses, pulse trains, pulse
bursts, burst patterns, or other patterns, and may include various
duty cycles. Accordingly, the first and second period of time may
generally refer to a period of time during which stimulation is
actively delivered via a given electrode combination, even though
stimulation may be delivered in different forms. Again, the first
and second electrical stimulation therapies are configured to
produce a substantially identical therapeutic result. In some
cases, the first and second periods of time may be the same or
different, and may partially overlap or not overlap with one
another. If the first and second periods of time do not overlap,
they may be separated by a gap in time or be arranged such that the
second period of time commences immediately upon termination of the
first period of time. In addition, the first and second periods of
time may be greater than or equal to thirty seconds, greater than
or equal to one minute, greater than or equal to five minutes,
greater than or equal to ten minutes, greater than or equal to one
hour, or greater than or equal to one day.
Again, delivery of the first and second gastric electrical
stimulation therapy may be time-interleaved or time-independent.
For example, different pulses or bursts of pulses or burst patterns
may be delivered via electrode combinations at different positions
on a time-alternating basis within a given therapy period or
therapy window. Alternatively, different therapy periods or therapy
windows may use different electrode combinations at different
positions on a time-independent basis. In this latter case, instead
of alternating between different positions, delivery of stimulation
is generally time-independent in that stimulation may be delivered
at a single given position for substantially an entire therapy
period or window. Then, in a subsequent therapy period or window,
stimulation may be delivered at a different, single given position
for substantially the entire subsequent therapy period or window.
In this case, delivery of stimulation is time-independent in the
sense that there is no alternating of therapy at different
positions within a given therapy period or window.
In summary, different electrode sets implanted at different
locations on an applicable gastrointestinal organ, such as the
stomach, may be used in different therapy periods, e.g., hours, or
days, at different times within a given therapy period, or on
alternating multi-channel, multi-site basis. Also, electrodes in
one array 54 may be used for an extended period of time such as
several seconds, minutes, hours, days or weeks, followed by
transition to electrodes on the other array 56 after the extended
period of time. In some cases, delivery of stimulation to one
electrode set may at least partially overlap with delivery of
stimulation to the other set of electrodes. However, at least
portions of the stimulation delivered to the first and second
electrode sets may not overlap. In other words, the first period of
time for which stimulation is delivered to the first electrode set
may either partially overlap or not overlap with the first period
of time for which stimulation is delivered to the second electrode
set. In each case, the stimulation delivered via the various
electrodes is configured to support substantially the same
therapeutic effect, such as gastric distension. Yet, the first and
second electrode sets are displaced from one another by a
sufficient distance so that different tissue sites receive the
stimulation. As examples, electrodes in array 54 may be displaced
from electrodes in array 56 by at least approximately 1 cm, more
preferably at least approximately 3 cm, and still more preferably
at least approximately 5 cm.
FIG. 5A is an example timing diagram illustrating a continuous
train 59 of pulses that may be used in electrical stimulation
delivered to patient 12. FIGS. 5B, 5C and 5D are example timing
diagrams illustrating bursts of pulses that may be delivered as
burst patterns in the electrical stimulation delivered to patient
16. As shown in FIG. 5B, electrical pulses generated by stimulator
12 may be delivered to patient 16 in bursts of pulses, where each
pulse includes n pulses, and n is greater than one. The pattern of
bursts may be a regular pattern or an irregular pattern. In
addition, as shown in FIG. 5B, a burst pattern comprises multiple
pulse bursts. FIG. 5C illustrates delivery of single burst patterns
that generally conform to therapy windows. FIG. 5D illustrates
delivery of multiple burst patterns within given therapy
windows.
Each burst 62 includes multiple electrical pulses. In the example
of FIG. 5B, T.sub.on is the time that stimulator 12 delivers
continuous pulses that make up each burst 62, while T.sub.off is
the time stimulator 12 is not delivering pulses between each burst
62. The ratio of T.sub.on to T.sub.off is the duty cycle of burst
pattern 60 that is set by the clinician to provide effective
therapy. The duty cycle of burst pattern 60 may be set anywhere
between 0% and 100% ON. However, generally the duty cycle may be
less than 50% ON and more than 50% OFF. Hence, a continuous train
of pulses can be gated ON to form a pulse burst. Likewise, a series
of pulse bursts may be gated ON to form a burst pattern 60
containing multiple pulse bursts 62. Stimulation may be delivered,
in various embodiments, as pulses, bursts, burst patterns,
continuous pulse trains, or the like.
While FIG. 5B illustrates each burst 62 having eight pulses and
burst pattern 60 having seven bursts for purposes of illustration,
any number of pulses and bursts 62 may define one burst pattern 60.
For example, burst pattern 60 may include over one hundred bursts
while each burst 62 may include more than 20 pulses. Alternatively,
burst pattern 60 may include fewer bursts 62 with each burst having
fewer pulses. A clinician may program stimulator 12 to deliver
burst pattern 60 to patient 16 with the desired number of bursts 62
and pulses to treat patient 16. The pulses of bursts 62 and each of
the bursts may be delivered according to example stimulation
parameters described herein.
FIG. 5C illustrates an example therapy schedule time period P that
includes multiple therapy applications within therapy windows W.
Hence, one or more therapy windows W may be applied during a
therapy schedule time period P. For example, period P may be equal
to a 24 hour day of patient 16, e.g., from midnight to midnight. In
the examples of FIGS. 5C and 5D, the lockout period L prevents
stimulator 12 from delivering stimulation within a predetermined
period of time following termination of stimulation. In this
manner, lockout period L, whether maintained by stimulator 12 or
patient programmer 14, functions as an anti-desensitization feature
by preventing continuous or excessive delivery of stimulation.
Instead, stimulation is generally delivered when needed, rather
than at times when the stimulation is not necessary, such as
between meals or while the patient is sleeping. In addition,
stimulator 12 and/or patient programmer 14 may implement additional
anti-desensitization features in the form of therapy windows and a
therapy schedule.
As shown in FIGS. 5C and 5D, delivery of therapy may be permitted
only during schedule times S permitted by a therapy schedule. Times
S may be substantially coincident with meal times and, optionally,
snack times. Each time S may extend over a period of time in which
it is likely that the patient may ingest a meal. For breakfast, for
example, the time S may run from 6 am to 8 am. As mentioned
previously, times S on the therapy schedule may have start and/or
end times and/or durations that vary from day to day, as another
anti-desensitization feature. If therapy is requested during a
schedule time S, then therapy may be delivered, e.g., by
transmission of a command from patient programmer 14 to stimulator
12, subject to other anti-desensitization features. If therapy is
requested outside of one of the schedule times S, however, than
delivery of therapy is not permitted, either by refusal of
programmer 14 to transmit a request or refusal of stimulator 12 to
deliver stimulation in response to a request from the
programmer.
With further reference to FIG. 5C, a therapy window W specifies a
maximum time for which therapy may be delivered. In this manner,
the therapy window W limits the duration for which stimulation is
delivered at a given time. As mentioned previously, the therapy
window W may selected based on a first period of time that is found
to be sufficient to cause a desired physiological response or
therapeutic result for a second period of time. The second period
of time may be greater than or less than the first period of time,
but extends at least in part beyond the end of the first period of
time. The first period of time may be selected to produce the
desired therapeutic effect for the second period of time and, in
some cases, may be the minimum period of time sufficient to produce
the desired therapeutic effect for the second period of time.
In the case of gastric distention, for example, the desired
therapeutic effect, response or result may be a maintenance of an
increase in gastric volume at a threshold percentage of a target
level, e.g., a 50% volume increase above a baseline level of
gastric volume. Programmer 14 and/or stimulator 12 may start a
clock or other timing device upon initiation of delivery of therapy
and then require termination of therapy prior to expiration of an
applicable therapy window W, which corresponds to the first period
of time sufficient to produce the desired therapeutic effect for
the second period of time. In this manner, any single
administration of therapy is limited in time by the therapy window
W in order to reduce the likelihood of desensitization, and
possibly conserve power resources. As described above, the therapy
window W may be selected to be the approximately the minimum time
necessary to achieve a desired therapeutic effect for a desired
period of time, i.e., the second period of time, given a set of
stimulation parameters and/or other factors.
Alternatively, the therapy window W may be approximately this
minimum time plus an optional margin such that the therapy window W
is somewhat greater than or equal to the minimum. In any event, the
therapy window is a function of an approximate duration of the
gastric electrical stimulation therapy that is effective in
producing a desired therapeutic effect for a desired period of time
during and after termination of the gastric electrical stimulation
therapy. Notably, the therapy window may be shorter than the
desired period of time for which the therapeutic result is produced
because the recovery time of the tissue may permit the therapeutic
result to be prolonged to a desired degree for an extended period
of time following termination of delivery of stimulation.
The length of the therapy window W, like the lockout period L and
scheduled time S may be the same throughout the day, or may vary
for different meals. For example, a patient 16 may desire a longer
schedule time S for dinner, to permit flexible dinner planning.
Also, the therapy window W may be increased for some meals, such as
dinner, which may have a more leisurely pace to provide an extended
period in which the desired therapeutic effect is available. If
therapy starts within a schedule time S, the therapy may be
permitted to extend beyond the schedule time S, subject to the
maximum time specified by the therapy window W. Alternatively,
therapy may be terminated at the end of the scheduled time S if it
would extend beyond the scheduled time S.
In some embodiments, each therapy application within a therapy
window W may contain one or more burst patterns 60 containing
multiple bursts 62. A single burst pattern 60 may reside within
each therapy window W and form the therapy application for a
particular therapy schedule time period S. Alternatively, a therapy
window W may include multiple burst patterns 60, e.g., as shown in
FIG. 5D. Each time that therapy is delivered to patient 16,
stimulator 12 delivers bursts of pulses as described above for
burst pattern 60.
The beginning of each therapy application in a therapy window W may
be related to when patient 16 eats a meal, and may be either
initiated by patient 16 or scheduled by stimulator 12. When
initiated by a patient, delivery of the therapy is permitted within
a permitted time S, per the therapy schedule. The therapy may be
initiated at any time within the time S, and need not be at the
beginning of the time S. Once started, however, the therapy
generally is limited to the duration of an applicable therapy
window W, e.g., to avoid or reduce desensitization and/or conserve
power.
As shown in FIG. 5C, stimulator 12 delivers therapy to patient 16
during times T.sub.2, T.sub.4 and T.sub.6. During times T.sub.1,
T.sub.3, T.sub.5, and T.sub.7, no electrical stimulation is
delivered to patient 16. At the end of each therapy application,
which is coincident with a therapy window W, system 10 implements
lockout period L to prevent stimulator 12 from delivering therapy
to patient 16 until lockout period L has elapsed, either by
directly locking out stimulator 12 from delivery therapy or locking
out patient programmer 14 from transmitting a command to initiate
delivery of therapy during the lockout period. In addition, after
the end of each therapy window W, a desired therapeutic effect may
remain in effect for some time.
Therapy windows W and burst patterns 60 may be substantially
equivalent with one another throughout period P or different.
Likewise, lockout periods L may be substantially equivalent
throughout period P or different. As an alternative, in some cases,
therapy windows W and burst patterns 60 may change in timing and/or
duration. For example, timing and/or duration of burst patterns 60
may change depending upon the time of day the therapy is started.
If multiple burst patterns, each containing multiple pulse bursts,
are delivered within an applicable therapy window, the timing
between successive burst patterns may be fixed or variable. If the
timing is variable, the time between burst patterns may be the same
throughout a given burst pattern. Alternatively, the times between
different burst patterns in a given window W may vary. In addition,
the duration of burst patterns delivered to the patient may vary
among different therapy windows, or within a given therapy window.
Also, the durations of burst patterns may vary among different
therapy windows, or within a given therapy window.
As an illustration, for purposes of example and without limitation,
a particular therapy window could include x burst patterns. Each
burst pattern could include y pulse bursts. Each pulse burst could
include z pulses. Each burst pattern could have a duration of time
t.sub.1, and be separated in time by time t.sub.2. In operation,
the number x of burst patterns could be varied from therapy window
to therapy window. The number of bursts y and pulses in each burst
z could likewise be varied. In addition, the times t.sub.1 and
t.sub.2 could be varied from therapy window to therapy window or
within a given therapy window such that some burst patterns in a
window have different durations, and such that the time between
successive burst patterns in a window is different.
FIG. 5D shows multiple burst patterns provided in successive
therapy windows. For example, four burst patterns 60A of equal
duration and equal time spacing between successive burst patterns
are provided in a first therapy window W at time T.sub.2. Three
burst patterns 60B of different durations and different time
spacing are provided in the next therapy window W at time T.sub.4.
Four burst patterns 60C of equal duration but different time
spacing are provided in the therapy window W at time T.sub.6.
Hence, multiple types of variation may be introduced into the burst
patterns to provide further variation that may prevent or delay
desensitization of stimulated tissue in patient 16.
With further reference to FIGS. 5C and 5D, lockout period L may
also be vary, e.g., as a function of the time of day. For example,
lockout periods L may be shorter in duration during the morning
while lockout periods L in the evening may be longer to prevent
patient 16 from sleeping with undigested food in stomach 22. In
addition, times between successive therapy applications may vary
due to when patient 16 eats. As shown in FIG. 5C, time T.sub.5 is
greater than times T.sub.1, T.sub.3 and T.sub.7. In other examples,
period P may include more or less than three burst applications, as
needed by patient 16 and allowed by the clinician.
FIG. 5E shows delivery of various burst patterns throughout a
period P. Whether lockout periods L, schedule times S, and therapy
windows W are used or not, FIG. 5E illustrates delivery of
stimulation using burst patterns that may vary in number, duration
and/or timing from period to period P. In a first period P, for
example, burst patterns may be delivered as indicated by 60D, 60F
and 60H. In a second period P, burst patterns may be delivered as
indicated by 60E, 60G, 60I, and 60J. As shown in FIG. 5D, the burst
patterns may be delivered with different start times and durations.
In addition, the number of burst patterns may vary from period to
period, e.g., as shown by burst pattern 60J.
Although a relatively small number of burst patterns are shown in
FIG. 5E, a much larger number of burst patterns may be delivered.
As one example, programmer 14 and/or stimulator 12 may be
configured to deliver burst patterns having durations of 1 to 60
minutes, with a number of burst patterns per 24-hour period being
variable from 1 to 100 burst patterns. By varying the timing,
duration and number of burst patterns from period to period,
desensitization can be prevented or delayed. In addition,
desensitization can be prevented or delayed by delivering multiple
burst patterns at different times and with different durations
within a given period. In some embodiments, the number, timing and
duration of burst patterns may be specified by a clinician or
permitted to vary automatically, e.g., randomly, within limits
specified by the clinician via a physician programmer, according to
a randomization algorithm or other algorithm used by programmer 14
and/or stimulator 12.
FIG. 5F is a graph illustrating gastric distention during and
following application of stimulation within a therapy window. The
graph of FIG. 5F is provided for purposes of illustration and
depicts the concept of a therapy window and associated gastric
distention response. Accordingly, FIG. 5F does not represent actual
data and is not drawn to scale. In the example of FIG. 5,
stimulation is delivered for a first period of time T1=t4-t1,
consistent with a therapy window. In particular, following an
initial time t0, stimulation is delivered at time t1 and maintained
until time t4 During stimulation, gastric volume increases, and
reaches a therapeutic threshold (defined here as a gastric volume
that is 50% greater than gastric volume at baseline t0) at time t2,
and at a later time t3, reaches a maximum level.
Delivery of stimulation may continue until time t4. When
stimulation is terminated at time t4, gastric volume gradually
decreases, reaching the threshold for therapeutic efficacy (the
therapeutic threshold) at time t5. By time t6, gastric volume has
decayed back to baseline levels obtained at t0. Thus, by applying
stimulation for a time T1, gastric volume is increased over
baseline levels to a therapeutic range for a time T2. As the time
for increasing gastric volume after the onset of stimulation is
generally greater than the time for gastric volume to return to
baseline levels after termination of stimulation, T2 will generally
be greater than T1.
Note that, in this discussion, gastric volume is used as an example
of a measure of muscle tone. Other terminology may also be used
interchangeably including gastric distention, gastric tone, gastric
volume, gastric relaxation. Other measures of gastric relaxation
may include changes in length of any segment of the stomach, or the
thickness of the stomach muscle wall, as measured by ultrasound,
magnetic, mechanical, optical, or other electronic transducers;
In the example of FIG. 5F, the gastric stimulation produces an
increase in gastric volume relative to an initial volume prior to
stimulation. After stimulation is stopped at time t4, the gastric
volume does not immediately return to the initial volume. Rather,
gastric volume decays somewhat slowly such that gastric volume
remains above the target threshold level (i.e., a volume that is
50%.gtoreq.baseline volume) achieved by stimulation until time t5.
If the desired therapeutic effect occurs when gastric volume
remains above the target threshold level (i.e., gastric volume
remains.gtoreq.50% above baseline gastric volume), then the desired
therapeutic effect persists for an additional time t5-t4 following
cessation of stimulation. Hence, stimulation for a first period of
time T1=t3-t1 can produce a desired therapeutic effect for a second
period of time T2=t5-t2, wherein T2 is greater than T1.
FIGS. 6A, 6B and 6C are example timing diagrams illustrating
continuous pulses and bursts of pulses delivered to patient 16 when
system 10 delivers therapy to multiple distinct sites, i.e., via
multiple, different physical channels, as part of a multi-site
anti-desensitization feature. Such channels may be realized by
different electrodes and associated conductors within leads 18, 20
that can be selected to deliver therapy. Channels 1 and 2 will be
described herein as example channels that deliver stimulation
therapy. Channels 1 and 2 may both indicate stimulation delivered
to the same organ such as stomach 22 or the small intestine via
respective electrode combinations. The small intestine may be
stimulated, e.g., at the duodenum or the jejunum, for example. The
stomach may be stimulated, e.g., in the lesser or greater
curvature.
FIG. 6A illustrates a timing diagram for two channels, channel 1
and channel 2. Channels 1 and 2 deliver stimulation to a different
electrode combinations. In the example of FIG. 6A, channel 1
delivers bursts 66 of discrete pulses over time while channel 2
delivers a continuous train of pulses. Pulses delivered by channel
1 and channel 2 may have the same parameters or different
parameters, depending upon the tissue treated by channels 1 and 2,
and may be delivered together within the same therapy window.
However, the stimulation delivered via channel 1 and channel 2 is
selected to produce substantially the same therapeutic effect.
FIG. 6B shows bursts 68 of pulses on channel 1 and bursts 70 of
pulses on channel 2 for multi-site gastric stimulation. Pulse
bursts 68 and 70 are shown in synchronous burst mode such that
bursts 68 and 70 have equivalent duty cycles. Bursts 68 and 70 are
offset from each other in time, such that they are delivered on an
alternating basis, but the bursts may also be delivered at the same
time in some example embodiments. Bursts 68 and 70 are delivered
during the ON portion of the duty cycle. Pulse bursts 68 and 70 may
be delivered in a variety of different modes, such as a continuous
mode, an asynchronous burst mode, or a synchronous burst mode. In a
continuous mode, the pulse train is delivered relatively
continuously over an active period in which stimulation is "ON." In
an asynchronous burst mode, the pulse train is delivered in
periodic bursts during the active period. The continuous and
asynchronous burst modes do not rely on synchronization between
channels 1 and 2.
In a synchronous burst mode, the pulse train is delivered in bursts
that are synchronized with multiple channels, such as channels 1
and 2. In this sense, the synchronous burst mode may be viewed as a
closed loop approach. Stimulator 12 may synchronize electrical
stimulation between channels 1 and 2 in order for the resulting
organ response to stimulation to be matched for maximal efficacy.
Channels 1 and 2 may activate stimulation to cause gastric
distention and thereby discourage the intake of excessive amounts
of food. In the example of FIG. 6B, the alternating bursts may be
delivered on a time-interleaved basis within the same therapy
window. The duration of each burst may be greater than or equal to
approximately thirty seconds. By shifting between different
electrode combinations on a time-interleaved basis, a multi-site
stimulation feature may reduce tissue desensitization.
FIG. 6C illustrates alternating burst patterns 72 and 74 between
different electrode combinations on channels 1 and 2. Each of burst
patterns 72 and 74 includes multiple bursts of electrical pulses,
e.g., like bursts 68 or 70 of FIG. 6B. The alternating burst
patterns 72, 74 may be delivered on a time-interleaved basis within
the same therapy window. Burst patterns 72 and 74 may be referred
to as alternating synchronous burst patterns because stimulator 12
only delivers one of burst patterns 72 and 74 at any given time. In
some examples, bursts 72 and 74 may be provided such that the burst
patterns on channels 1 and 2 overlap or are separated by a certain
interval. The duration of each burst pattern may be greater than or
equal to approximately thirty seconds.
Hence, FIG. 6A shows channel 1 delivering pulse bursts and channel
2 delivering continuous pulses, FIG. 6B shows synchronous delivery
of pulse bursts on an alternating basis between channel 1 and
channel 2, and FIG. 6C shows synchronous delivery of burst
patterns, each containing multiple pulse bursts, on an alternating
basis between channel 1 and channel 2. In each case, stimulator 12
may use multi-cite stimulation on channel 1 and channel 2 as an
anti-desensitization feature to prevent or delay sensitization of a
tissue site. The pulses, bursts, or burst patterns may be delivered
to different electrode combinations at different times to reduce
desensitization.
With multi-site stimulation, stimulator 12 may deliver essentially
the same type of stimulation to achieve essentially the same type
of therapeutic effect via two or more different physical channels
(i.e., two different electrode combinations) to two different
stimulation sites with the same or similar stimulation parameters.
As an example, stimulator 12 may deliver stimulation with similar
parameters to two different tissue sites on an alternating basis.
The parameters may be selected such that the stimulation of the
different tissue sites, while preventing or delaying
desensitization, produce a desired overall therapeutic effect, such
as gastric distension or regulation of motility.
Stimulation parameters may be identical or differ slightly for
electrodes stimulating different tissue sites. In either case,
however, it is desirable that the parameters of stimulation
delivered on channels 1 and 2 be selected to achieve substantially
the same therapeutic effect. If gastric distention is desired, for
example, then stimulation parameters on channels 1 and 2 may be
selected to support gastric distention, and preferably similar
amounts of gastric distention.
Although two channels are described for purposes of illustration,
stimulator 12 may apply stimulation via three, four or more
channels for multi-site stimulation to achieve similar therapeutic
effects. For example, stimulator 12 may be coupled to multiple
leads to deliver stimulation to different electrodes on the
multiple leads. Alternatively, stimulator 12 may select multiple
electrode combinations available using electrodes deployed on a
single implantable lead.
Stimulator 12 also may distribute pulsed stimulation therapy to at
least one of multiple tissue sites, e.g., via channels 1 and 2, in
order to provide another anti-desensitization feature to patient
16. Delivery of pulse bursts or burst patterns to multiple
stimulation sites on an alternating basis may be preferred so that
none of the stimulation sites receives continuous stimulation.
Instead of providing substantially continuous electrical pulses to
stomach 22 via one channel, stimulator 12 may spread out the
electrical stimulation to multiple tissue sites via channels 1 and
2, where each channel includes electrodes positioned at different
tissue sites. The resulting therapy may be effective in causing
gastric distention or other desired effects, but prevents or delays
desensitization of the tissue that could otherwise result from
delivering continuous pulses to the same tissue site on a
persistent basis. Instead, the tissue site receives stimulation
intermittently, according to any of the multi-channel pulse or
burst approaches illustrated in FIGS. 6A-6C.
FIGS. 7A, 7B, 7C, 7D, and 7E are example timing diagrams
illustrating relative timing of stimulation delivered via different
channels in association with a multi-site stimulation feature. In
the examples of FIGS. 7A-7E, first, second and third channels
deliver first, second and third electrical stimulation therapy to a
gastrointestinal organ via first, second and third electrode
combinations, respectively. The first, second and third electrode
combinations are associated with first, second and third positions
on the gastrointestinal organs. The first, second and third
stimulation therapy are delivered for first, second and third
periods of time, respectively, where each period of time is greater
than approximately thirty seconds, greater than or equal to one
minute, greater than or equal to five minutes, greater than or
equal to ten minutes, greater than or equal to one hour, or greater
than or equal to one day. The first, second and third stimulation
therapies are configured to produce a substantially identical
therapeutic result, such as distention. The first, second, and
third period of time may partially overlap or not overlap, and may
be same or different durations.
As shown in FIG. 7A, first, second and third stimulation therapies
75, 77, 79 may be delivered on Channels 1, 2, and 3, respectively,
to selected electrode combinations, e.g., as pulses, bursts, burst
patterns, or continuous pulse trains. In the example of FIG. 7A,
the stimulation 75, 77, 79 on each channel is ordered such that
first stimulation 75 on Channel 1 is delivered for a first period
of time t1, second stimulation 77 is then delivered for a second
period of time t2 after the first stimulation is stopped, and third
stimulation 79 is then delivered for a third period of time t3
after the second stimulation is stopped. In this example, the
stimulations on Channels 1, 2 and 3 do not overlap. Instead,
stimulation on one channel starts upon cessation of stimulation on
another channel. However, overlapped stimulation may be used in
other embodiments. Also, in FIG. 7A, stimulation one channel starts
immediately upon cessation of stimulation on the previous channel.
In other embodiments, however, a time gap may be provided between
successive stimulations on different channels.
In FIG. 7A, stimulation is ordered such to apply first stimulation
75 on Channel 1, followed by second stimulation 77 on Channel 2,
followed by third stimulation 79 on Channel 3. In the example of
FIG. 7B, however, the order is changed to apply first stimulation
75 on Channel 1, followed by third stimulation 79 on Channel 3,
followed by second stimulation on Channel 2. The order may be fixed
or varying and may be selected by a physician. In some cases, a
randomization or pseudo-randomization function may be applied to
select the ordering of the Channels. In each case, the stimulation
delivered on each channel may be greater than approximately thirty
seconds.
The positioning of the electrode combinations associated with
Channels 1, 2 and 3 may be unrelated to the ordering. For example,
in some cases, the first, second and third positions may be
arranged such that the first position is most proximal on the
gastrointestinal organ, the third position is most distal on the
gastrointestinal organ, and the second position is between the
first and third positions, yet stimulation need not be applied
along a particular axis relative to the gastrointestinal organ. In
general, there are no restrictions on alignment or orientation of
different electrodes with respect to the GI tract. In particular,
the electrodes do not need to be positioned or aligned to produce a
functional peristaltic activity. The stimulation ordering and
positioning of the multiple electrode combinations may be flexible.
Accordingly, the ordering need not be related to the positions of
the electrode combinations on the gastrointestinal organ,
particularly where stimulation is configured to produce distention,
nausea or discomfort, and not to regulate motility by peristaltic
function.
In the example of FIG. 7C, first and second stimulation 81, 83 are
applied via Channel 1 and Channel 2, respectively, with a time
delay between cessation of delivery of the first stimulation
delivery and the start of delivery of the second stimulation, and
vice versa. Hence, in contrast to the example of FIGS. 7A and 7B,
the next stimulation does not commence immediately following the
previous stimulation. Instead, there may be a delay between
stimulation via different electrode combinations. The delay may be
greater than approximately one second, ten seconds, thirty seconds,
one minute, or longer.
FIG. 7D shows the delivery of first and second stimulation 85, 87
via different electrode combinations associated with Channels 1 and
2 within the same therapy window W on a time-interleaved basis. In
this case, stimulation delivered during a therapy window, as
described herein, is provided by stimulation from two or more
Channels, which are time-interleaved with one another within the
therapy window. In the example of FIG. 7E, however, first and
second stimulation 89, 91 are delivered via different electrode
combinations associated with Channels 1 and 2 within different
therapy windows W on a time-independent basis. For example, first
stimulation may be delivered via a first electrode combination for
a first period of time associated with an entire therapy window W,
and then second stimulation may be delivered via a second electrode
combination for a second period of time associated with an entire,
different therapy window.
Again, the first and second stimulation therapies may comprise
pulses, pulse trains, pulse bursts, burst patterns, or other
patterns, and may include various duty cycles. The first and second
periods of time may generally refer to a period of time during
which stimulation is actively delivered via a given electrode
combination, even though stimulation may be delivered in different
forms. Accordingly, delivery of stimulation for a period of time
does not necessarily require that stimulation pulses are delivered
continuously during that time. Rather, it is sufficient that
stimulation be actively delivered, subject to gaps or delays
associated with pulses, bursts, burst patterns or other waveforms
that may be specified for the stimulation, e.g., as stimulation
parameters.
FIGS. 8A, 8B and 8C are example timing diagrams illustrating bursts
of pulses having variations between the pulses of the bursts. As
shown in FIG. 7A, burst pattern 76 includes multiple bursts 78A,
78B, 78C, 78D and 78E (collectively "bursts 78) of discrete pulses.
Burst pattern 76 and bursts 78 may be similar to burst pattern 60
and bursts 62, respectively, as described in FIGS. 5A and 5B. Burst
patterns as shown in FIGS. 8A-8C may be used in conjunction with
other anti-desensitization features, such as multi-site
stimulation, therapy windows, and lockout intervals. The pulses of
each of bursts 78 may vary in voltage amplitude within each burst
such that at least two pulses within each burst have different
voltage amplitudes. In addition, each subsequent burst may contain
a sequence of pulses that is not identical to the sequence of
pulses of the previous burst. These variations in voltage amplitude
of the pulses may help to prevent or delay desensitization. For
example, the pulses of burst 78A are not identical to the pulses
delivered during burst 78B. While voltage amplitude is the
stimulation parameter described in FIGS. 8A, 8B and 8C, the pulses
may vary by any stimulation parameter, such as current amplitude,
pulse width, or pulse rate.
The pulses of bursts 78 vary within each burst randomly within a
predetermined range. The resulting pulses may have any voltage
amplitude within the range in order to vary the stimulation
therapy. In other examples, the variation between pulses may be
limited according to a weighted randomization to a target magnitude
and/or limited to the magnitude of change between consecutive
pulses. For example, the weighted randomization may generate pulses
with a large percentage of pulses having a voltage amplitude near
the target magnitude. Alternatively, the difference in magnitude
between subsequent pulses may be limited to a predetermined value
or a percentage of the preceding pulse.
In addition to varying of voltage amplitude between pulses within
each burst 78, bursts 78 of burst pattern 76 may contain pulses
having different voltage amplitudes between subsequent bursts. In
this manner, variation of voltage amplitude between pulses
continues into subsequent bursts in order to produce bursts having
continually changing pulses. In alternative embodiments, burst
pattern 76 may only have variations in pulse voltage amplitude
between pulses of the same burst. In other words, burst 78A has at
least two pulses with different voltage amplitude and burst 78A is
then repeated throughout burst pattern 76. Further, some other
examples of burst pattern 76 may include at least two bursts having
identical pulses.
FIG. 8B shows burst pattern 80 having multiple bursts 82A, 82B,
82C, 82D and 82E (collectively "bursts 82"). Burst pattern 80 is
similar to burst pattern 76. However, bursts 82 of burst pattern 80
each may have pulses of the same voltage amplitude within each of
the bursts. A anti-desensitization measure implemented in burst
pattern 80 is that the voltage amplitude of the pulses only varies
between subsequent bursts, not within any burst. As shown in FIG.
8B, the voltage amplitude of the pulses in burst 82A is smaller
than the voltage amplitude of the pulses in burst 82B. In this
manner, the tissue affected by the stimulation pulses may not
become desensitized to bursts having the same voltage amplitude
throughout therapy. The variation in pulses provided within burst
pattern 80 may be governed by stimulator 12 in a similar manner as
described in FIG. 8A. In other examples of burst pattern 80, two or
more bursts may have pulses of the same voltage amplitude.
FIG. 8C shows multiple burst patterns 84A and 84B delivered to
patient 16. Stimulator 12 may implement a desensitization measure
that further varies the pulses of bursts throughout the treatment
of the patient. In some examples, burst pattern 76 and 80 described
above may be repeated whenever gastric stimulation is delivered to
patient 16. In contrast, burst patterns 84A and 84B of FIG. 8C
deliver bursts having pulses with different voltage amplitudes of
the pulses. Burst pattern 84A contains at least burst 86A and 86B.
The first burst 86A has pulses with smaller voltage amplitudes than
pulses of burst 86B. Burst pattern 84B is different than burst
pattern 84A such that first burst 88A has pulses with greater
voltage amplitudes than the pulses of burst 88B. While burst
patterns 84A and 84 may include two bursts or greater than one
hundred bursts, stimulator 12 or programmer 14 may vary at least
one burst between the two burst patterns in order to implement the
desensitization measure.
While the bursts shown in FIGS. 8A, 8B and 8C, each have six
pulses, bursts delivered to patient 16 may have any number of
pulses as desired by the clinician to treat the patient. In
addition, burst patterns 76, 80, 84A or 84B may have any number of
bursts. The number of bursts within subsequent burst patterns may
vary with the length of each burst pattern and/or the duty cycle of
the pulses and bursts. In any case, stimulator 12 may vary at least
one stimulation parameter within a burst, burst pattern, or
treatment of patient 16 in order to implement a desensitization
measure. This implementation is not directed to changing the
efficacy of therapy. Rather, the variation of stimulation
parameters is directed to extending the efficacy of therapy by
preventing the constant delivery of identical stimulation therapy
to a tissue site or sites.
FIG. 9 is a flow diagram illustrating a method for delivering
gastric stimulation therapy according to a lockout period that
extends the efficacy of the therapy. It will be apparent that the
method illustrated in FIG. 9 may be implemented within a patient
programmer, a gastric electrical stimulator, or a combination of
both. In general, one of the programmer or the stimulator receives
a request to deliver the electrical gastric stimulation therapy to
the patient, prohibits delivery of the gastric stimulation therapy
by the stimulator if the request is received within a lockout
period following a previous delivery of gastric stimulation
therapy, and permits delivery of the gastric stimulation therapy by
the stimulator if the request is not received within a lockout
period following the previous delivery of gastric stimulation
therapy.
As shown in FIG. 9, system 10 stands ready in standby mode where
the system is ready to deliver therapy when needed (90). If system
10 does not receive a request or indication for stimulation therapy
(92), the system remains in standby mode. If system 10 receives a
request to deliver stimulation (92), e.g., by user input into
patient programmer 14, a command received by stimulator 12 from
patient programmer 14, or a command generated automatically within
stimulator 12 or programmer 14, e.g., for delivery of stimulation
at a scheduled time, system 10 checks to determine if the
stimulation request is made at a permitted time on a therapy
schedule (94).
If not, then patient programmer 14 may deliver a prohibited time
message to patient 16 (96), advising the patient that stimulation
is not permitted. In this manner, patient programmer 14 or
stimulator 12 prohibit delivery of gastric stimulation therapy if a
request is not received within a time period specified by the
therapy schedule. The system 10 then may return to standby mode
(90). If the stimulation request is made at a permitted time (94),
then patient programmer 14 may determine if stimulation is
nevertheless locked out via a lockout period (98) following a
termination of a previous application of therapy. If system 10 is
locked out from delivering therapy, system 10 delivers a lockout
message to patient 16, e.g., via patient programmer 14, that
indicates therapy cannot be delivered at this time (100). System 10
then may return to standby mode (90).
If system 10 is not locked out, the system delivers electrical
stimulation to patient 16 via stimulator 12 (102). If a stop
request is received (104), e.g., from patient 16 via patient
programmer 14, the patient programmer instructs stimulator 12 to
stop stimulation (106). Similarly, if a stop request has not been
received but an applicable therapy window has expired (104),
patient programmer 14 instructs stimulator 12 to stop stimulation
(106). In this manner, stimulator 12 may receive an instruction
from programmer 14 to generate the stimulation for the first period
of time corresponding to the therapy window. Alternatively,
stimulator 12 may voluntarily stop stimulation if the stimulator is
configured to track the therapy window. If no stop request is
received, and the therapy window has not expired, stimulator 12
continues to deliver therapy (102). Again, the therapy window may
be selected to be a length of time sufficient to cause a desired
therapeutic effect for a desired period of time, taking into
account any prolonged therapeutic effect that may during a recovery
period following cessation of the stimulation therapy.
When stimulation is complete and stimulator 12 stops delivering
electrical stimulation to patient 16 (106), system 10 sets the
lockout period according to the lockout instructions stored by
system 10 (108), e.g., in patient programmer 14 or stimulator 12.
System 10 then any return to standby mode until stimulation therapy
is to be delivered again (90). In some embodiments, system 10 may
also implement additional anti-desensitization features to further
extend the efficacy of gastric stimulation therapy. For example, in
addition to the lockout, therapy schedule and therapy window
features, programmer 14 and/or stimulator 12 may deliver
stimulation using burst pattern parameter selection, a burst
pattern variation feature, or multi-site features.
FIG. 10 is a flow diagram illustrating a method for delivering
gastric stimulation therapy according to a selection of electrode
combinations to extend the efficacy of the therapy. It will be
apparent that the method illustrated in FIG. 10 may be implemented
within a patient programmer, a gastric electrical stimulator, or a
combination of both. As shown in FIG. 10, system 10 remains in
standby mode until a request for stimulation delivery is received
(110). The request may be a patient input that requests stimulation
therapy, which may be entered into patient programmer 14.
Alternatively, the request may be a command transmitted by patient
programmer 14 to stimulator 12. As a further alternative, the
request may be a command generated automatically within patient
programmer 14 or stimulator 12. In this example, system 10
generates a selection of electrodes, either in patient programmer
14 or stimulator 12, by automatically selecting new, available
electrodes for electrical stimulation (112) according to a
predetermined order, a random selection function, or a
pseudo-random selection function. The electrodes may be selected
from one or more arrays of multiple electrodes, e.g., as shown in
FIG. 4, to form different electrode combinations for use in
multi-site stimulation.
Random or pseudo-random selection may be used within programmer 14
and/or stimulator 12 to produce a selected combination of
electrodes for delivery of stimulation. Alternatively, instead of
random or pseudo-random selection, system 10 may select the
electrodes according to a predetermined progression or scheme,
which may be defined by a clinician. In either case, the selection
is automatic by programmer 14 or stimulator 12. The electrode
selection may be made by patient programmer 14, in which case the
patient programmer transmits the selection to stimulator 12 for use
in delivery of stimulation. Alternatively, stimulator 12 may
voluntarily select the electrodes when patient programmer 14
instructs the stimulator to start stimulation. In each case, the
electrode selection may be subject to constraints such that
electrodes selected at different tissue sites are still sufficient
to achieve a desired therapeutic effect.
The new electrodes associated with a newly selected electrode
combination should be different from the electrodes in the
electrode combination used for the last stimulation application,
and should target a different stimulation site. The last
stimulation may refer to stimulation delivered in a previous
scheduled period S on the therapy schedule, during a previous
therapy window W, during a previous time segment within a therapy
window, or otherwise. For example, the electrode combination
selection may be changed from one therapy window to another such
that successive applications of stimulation therapy use different
electrode combinations. Alternatively, the electrode selection may
be changed from one scheduled time period to another, e.g., such
that a patient receives stimulation via different electrodes at
breakfast, lunch, dinner or other time periods.
The process of FIG. 10 also may be applicable to techniques that do
no make use of therapy schedules, therapy windows, or the like. As
an alternative, different sets of electrodes may be selected as
electrode combinations for successive applications of stimulation,
without regard to the manner in which the timing of the stimulation
is determined. In each case, use of the same electrodes as
electrode combinations is avoided for consecutive stimulation
applications. In addition, the electrode selection may be changed
for one pulse burst to another or for one burst pattern to another
within the same therapy window or scheduled time period. As a
further alternative, electrode selection may be changed at periodic
intervals during the course of delivery of stimulation, e.g., every
n seconds or minutes. Each electrode combination may be used to
deliver stimulation for a period of time of greater than or equal
to thirty seconds.
Stimulator 12 delivers electrical stimulation to patient 16 via the
new selection of electrodes (114), either automatically or as
instructed by patient programmer 14. Once electrical stimulation is
complete (116), e.g., as a result of a patient request to stop
stimulation or expiration of a therapy window, scheduled time
period (FIG. 9), or other applicable time limit (such as a
specified period of time for use of the electrode combination),
stimulator 12 stops stimulation to cease therapy (118). Patient
programmer 14 then may store stimulation delivery information for
use or review at a later time (120). Stimulation delivery
information may include any data relevant to the therapy. For
example, stimulation delivery information may include stimulation
parameters such as voltage, current, pulse width, pulse frequency,
burst rate, and selection of electrodes. In addition, stimulation
delivery information may also include any patient input to patient
programmer 14, such as additional requests for stimulation or
changes in stimulation amplitude during therapy.
While random selection of electrode combinations may be useful,
patient programmer 14 may select electrode combinations based upon
any of a variety of methods desired by the clinician. For example,
patient programmer 14 may select electrodes by cycling through
available electrodes, selecting electrodes according to an
algorithm designed to limit desensitization of tissue, or some
other method. As one example, a clinician or other caregiver may
directly specify a fixed progression among successive, selected
electrode combinations. In any case, patient programmer 14 or
stimulator 12 changes the selection of electrode combinations to
support multi-site stimulation as another anti-desensitization
feature directed to extending the efficacy of the gastric
stimulation therapy. The selection of different electrode
combinations as an anti-desensitization feature, e.g., as
illustrated in FIG. 10, may be practiced independently or in
conjunction with other anti-desensitization features, e.g.,
lockout, therapy window, therapy schedule, and burst pattern
parameter selection.
FIG. 11 is a flow diagram illustrating a method for delivering
gastric stimulation therapy at with varying start times, end times,
or durations. The method of FIG. 11 may be implemented within
programmer 14 and/or stimulator 12 to adjust, e.g., timing and
duration of burst patterns, or timing and duration of permitted
time periods on a therapy schedule. As mentioned previously, start
times and/or end times associated with permitted time periods on a
therapy schedule may be adjusted. In this manner, the therapy
schedule may ensure that stimulation is delivered not only at
selected times, rather than continuously, but also at selected,
variable times. Also, as mentioned previous, the number, timing and
duration of burst patterns may be adjusted whether burst patterns
are used in conjunction with a therapy schedule and therapy
windows, or not.
In the example of FIG. 11, stimulator 12 or programmer 14 may
select a weighted randomized start time for the next stimulation
delivery (122), which may be coincident with the next permitted
period of time on a therapy schedule, if applicable. Processors
within stimulator 12 or programmer 14 may access instructions
within memory to perform the start time selection process. The
instructions may be in the form of a set of equations, for example,
that weight the start times to a target start time so that the
randomization of start times does not drift away from a preferred
start time for therapy. For example, the instructions may be
configured to generate a high percentage of start times within a
predetermined number of minutes (e.g., 10 to 15 minutes) of the
target start time. The clinician may alter the instructions at
initial programming or throughout therapy.
The selected start time may vary relative to the start time for a
previous stimulation delivery that was delivered, e.g., in a
previous period P. In particular, the start time of a previous
stimulation delivery in the same period P may not be relevant.
Rather, the start time may be selected so that stimulation is not
delivered at the same time during every period P, e.g., at the same
time every day. For example, the start time of stimulation
delivered around lunch time for a given day is varied relative to
the start time of stimulation delivery around lunch time the
previous day.
In addition to selecting a start time, stimulator 12 and/or
programmer 14 may determine an end time using a similar technique,
so that a duration of the stimulation delivery can be varied.
Alternatively, the duration may be fixed while the start time is
varied to change the timing of the stimulation delivery. Selecting
different start time and end time may be useful for varying the
timing and duration of burst patterns that are delivered with or
without regard to a therapy schedule or therapy windows.
Variation of start time and/or end time ensures that the next
stimulation delivery will not occur at the same time as the
corresponding stimulation delivery in the previous period P. For
example, if the corresponding start time was 9:05 AM the previous
day, stimulator 12 or programmer 14 may be programmed select a
start time so as to avoid a second day of starting therapy at 9:05
AM. Stimulator 12 or programmer 14 may store the selected start
and/or end time value(s) in memory to determine the start of the
next permitted period of time in the therapy schedule for delivery
of therapy (124).
Stimulator 12 or programmer 14 then uses the selected values to
define the next stimulation to be delivered (126). Therapy is then
delivered when an internal clock or other timing device indicates
that the time matches the selected start time in memory (128). If
the stimulation delivery is not complete (130), e.g., no stop
request, therapy window expiration, or therapy schedule time
expiration applies, stimulator 12 continues stimulation delivery
(128). Once stimulation is complete (130), stimulator 12 stops
stimulation delivery to patient 16 (132) and selects the next start
and/or end time value (122).
While stimulator 12 or programmer 14 are described in FIG. 11 as
using a weighted randomized start time, stimulator 12 may vary the
start time with any method desired by the clinician. For example,
the start times may be cycled between multiple reselected start
times, randomly selected within a given start time range, or
selected based upon several previous start times to ensure start
time variation. In any case, the variation of start times may
prevent the stimulated tissue from becoming accustomed to
stimulation at a certain static time during the day. In addition,
variation of start times may prevent patient 16 from altering their
eating habits to accommodate the stimulation therapy delivery
times.
FIG. 12 is a flow diagram illustrating a method for selecting
different burst pattern characteristics to extend efficacy of
therapy. As shown in FIG. 12, programmer 14 and/or stimulator 12
may select a variable burst pattern number (134), variable burst
pattern durations (136) and variable burst pattern start times
(138) for each therapy period or window. In this manner, different
numbers of burst patterns can be delivered in different therapy
periods, e.g., different days. In addition, the burst patterns on
different days may have different durations and start times.
Likewise, if stimulator 12 is configured to delivered more than one
burst pattern within a therapy window, the number, duration and
start times of the burst patterns may be varied. In this manner,
burst patterns can be modified to assist in preventing or delaying
desensitization.
FIG. 13 is a flow diagram illustrating application of a therapy
window feature as described herein for gastric electrical
stimulation to extend efficacy of therapy. In the example of FIG.
13, a period of time for a desired therapeutic effect is selected
(142). For example, a physician or patient may select the time of
the desired therapeutic effect to persist, e.g., via a programmer.
A programmer or stimulator determines a therapy window that is
sufficient to produce the desired therapeutic effect for the
selected period of time (144), e.g., given a set of stimulation
parameters. For example, the programmer or stimulator may refer to
preestablished data mapping the selected period of time to one of a
plurality of therapy windows, or apply a mathematical function that
computes a therapy window for the selected period of time. The data
or function may be formulated based on theoretical or empirical
data obtained for the patient or for a class of patients. Again,
different therapy windows, i.e., of different lengths, may be
predetermined for different therapeutic effects and different
periods of time for which the therapeutic effects are desired.
Accordingly, when a desired therapeutic effect is desired for a
particular period of time, the effect and the time can be mapped to
an appropriate therapy window using the preestablished mapping. The
stimulator then delivers the stimulation for the duration of the
therapy window (146) to produce the desired therapeutic effect for
the selected period of time, which extends beyond the end of the
therapy window.
FIG. 14 is a flow diagram illustrating application of a multi-site
stimulation feature as described herein for gastric electrical
stimulation to extend efficacy of therapy. In the example of FIG.
14, a programmer or stimulator configures first and second
stimulation therapies to produce a substantially identical
therapeutic result (148), such as distention. For example,
parameters associated with the first and second stimulation may be
programmed to produce the substantially identical therapeutic
result. In some cases, the parameters used for the first and second
stimulation may be substantially identical. The stimulator then may
apply the first and second stimulation to different sites via
different electrode combinations. As shown in FIG. 14, the
stimulator may deliver the first stimulation via a first electrode
combination for a first period of time greater than or equal to
approximately thirty seconds (150), and delivered the second
stimulation via a second electrode combination for a second period
of time greater than or equal to approximately thirty seconds
(152). The first and second periods of time may partially overlap
or not overlap, and may be the same or different in duration.
The techniques described in this disclosure may be implemented in
hardware, software, firmware or any combination thereof. For
example, various aspects of the techniques may be implemented
within one or more microprocessors, digital signal processors
(DSPs), application specific integrated circuits (ASICs), field
programmable logic arrays (FPGAs), or any other equivalent
integrated or discrete logic circuitry, as well as any combinations
of such components. The term "processor" or "processing circuitry"
may generally refer to any of the foregoing logic circuitry, alone
or in combination with other logic circuitry, or any other
equivalent circuitry.
When implemented in software, the functionality ascribed to the
systems and devices described in this disclosure may be embodied as
instructions on a computer-readable medium such as random access
memory (RAM), read-only memory (ROM), non-volatile random access
memory (NVRAM), electrically erasable programmable read-only memory
(EEPROM), FLASH memory, magnetic media, optical media, or the like.
The instructions are executed to support one or more aspects of the
functionality described in this disclosure.
Various aspects of the disclosure have been described. These and
other aspects are within the scope of the following claims.
* * * * *